Congratulations on the upgrade and thumbs up on the projector. Awesome little device. 
 

I think the HDMI out on the connector box should carry both sound and video. If that is the case, everything should work if you simply hook up the AMP to the HDMI out. The audio-return thing shouldn’t be relevant in that setup. 
 

If it doesn’t carry sound but only video, I think the easiest setup would be to split the signal from whatever you are connecting to the Projector’s connector box. I assume you have an Apple TV or something else hooked up to it?

If so, you can simply split the HDMI from that unit. One output will go to the projector and the other to the AMP.  It shouldn’t matter that the AMP receives both sound and video via HDMI - as long as it gets sound. 
 

Other than that, you can split a HDMI signal to video and optical and then you can get a HDMI-to-optical single for the AMP. You can get that on the Sonos website. 
 

The HDMI out will probably not work with the Beam as it is not listed as HDMI-ARC. You’ll need an adapter to extract the audio as optical, then feed that to the Beam via its adapter.

Or use the optical output of the (unspecified) source device.

@controlav is correct, except that OP is using an Amp, not a Beam, so will need to purchase the adapter separately.

https://www.sonos.com/en-us/shop/optical-audio-adapter.html

This is incorrect.  While HDMI is designed to carry video and audio signal, Amp and Beam don’t read the audio signal this way. “ARC” stands for Audio Return Channel, meaning audio is returning back along the cable in the opposite direction from the normal video/audio signal...and this is what the Amp reads.  

And to add on to that, source devices such as DVD and Blu-ray players, game consoles, cable and satellite boxes generally don’t create an HDMI-ARC signal at all. The electronics that create that signal is in the receiver, i.e the television, which takes the normal HDMI audio channel and returns it back out, hence the name Audio Return Channel. 
 

I do understand that the ARC stands for audio return. My understanding being that the tv would send any audio it receives and generates through the HDMI-ARC. Meaning that the port serves as both a normal input for video and audio and output for audio. Naturally, using a normal HDMI from a tv would not work, because these are inputs rather than outputs. 
 

I just assumed that the Beam and AMP would be able to pick up any audio from an HDMI-signal, so if a signal carrying video and audio was split in two, one could go to the Amp and the other to the projector. Surprised to learn that it is not the case.

Must try to hook up something directly to my Beam later just to “see” it with my own ears - but for now I stand corrected :)

As I understand it The Beam and the Amp use HDMI-ARC from a TV because that’s the only HDMI on a TV that’s not only an input (only used for a test image from my Beam) but also an output. If you connect a normal HDMI-output from, say, DVD-player tot a splitter and send the signal from the splitter to the beamer and to the Amp, you should have sound on the Amp. Is there something wrong with my reasonong?

Well the normal audio on HDMI and audio coming through ARC are actually different channels.  The can also even be different codecs in some cases.  And the HDMI port on the Amp and Beam are actually HDMI outputs, generating a screensaver on your TV.  Not sure if you can make a port operate as both an HDMI input and output.  Point being that there would be some additional development/testing for this to work both ways.

Perhaps the main reason Sonos didn’t implement connecting audio this way is to avoid confusion about how to setup Sonos.  Most people are not going to want to use a splitter, which is really the only way this other method would work since Sonos doesn’t have a 2nd HDMI port to pass video to a TV or projector.  Besides, HDMI-ARC or optical from the TV is the only way to get audio from TV smart apps.

Depends on what you mean by ‘signal’.  If you mean an optical connection then yes.  HDMI, then no.  HDMI-ARC doesn’t really sense for that connection either.

Yes, unfortunately, there is.

Unless the splitter has the technology built in it to ‘reflect’ the audio signal like the TV has, that won’t work. There is no HDMI-ARC signal in a normal HDMI feed.

OK. So ARC is technically different from the sound that comes with an image? 

Perhaps think of it as highway with many lanes (channels), and cars are equivalent to video, while trucks are equivalent to audio.   For a normal HDMI connection, all lanes going the same direction with some of them for cars only (video) and others for trucks (audio).  There is also a telephone wire going right alongside the highway for small two way communication….CEC (Consumer Electronic Commands) commands.  It’s the teephone wire that sends commands to devices to turn on/off, change volume etc.

For a connection using HDMI-ARC, you still have the same lanes for cars and truck going in the same direction, and you still have the telephone wire in place.  But you also have some additional truck only (audio) lanes going in the opposite direction.

When you have a Sonos Beam or Amp connected to your TV,  The Beam (technically HDMI output)  is sending out cars (video, in the form of a screensaver image) to the TV using the lanes (channels) describing above.  It could send out trucks as well, but does not.  It is using the telephone wire to communciate with the TV.  And it’s receiving trucks from the ARC lanes.  On the other end, the TV (technically HDMI input)  is receive cars (the screensaver, which it does not need to display) and trucks (audio,Sonos doesn’t send any).  It communicates with Sonos through the telephone line, telling it to change volume, receiving turn off commands, learning what codecs it can send, etc.  And the TV sends out trucks in the ARC lanes.

So why can’t the beam or amp get audio through normal HDMI?  Because it’s an HDMI output, not an input.  Because the flow of trucks on those lanes are supposed to go in the other direction..

It could be the same audio data, but a normal HDMI feed interleaves audio with video and control data. ARC sends only audio, in the reverse direction, via a dedicated pin.

That was also my thinking. Having worked with other receives with both HDMI in and out, I just assumed this to be the case.

But these guys are unfortunately right. I tried hooking up a Chromecast directly to my Beam Tonight and started streaming a tv-show to the Chromecast - but no sound.

Sound returned as soon as I switched the Beam back to getting its signal from my TV’s HDMI-ARC.

So as others have suggested, the OP will likely need an audio extractor to extract the audio an feed that to the AMP using the separate adapter or use the other inputs on the AMP.

 HDMI in and out through a single HDMI port?

Yes and no I guess.

As I understand it from the answers in this post, it’s an input in terms of sound but otherwise an output. 
 

If you have a look at many mid to high end receivers, they typically have one HDMI that goes to the TV and then several HDMI inputs so they work as HDMI-hubs.

You can then connect  game consoles, streaming boxes, Blu-ray players etc. to the receiver. 
 

The receiver will play audio from these inputs, send video from all these inputs to the tv as well as play any audio from the tv. I have attached an example.

Well, I’m not sure if it’s the official definition, but if you think of an HDMI port as IN or OUT in terms of video, then there are no IN/OUT HDMI ports.   None of the IN ports can send out video.  The single OUT port cannot take in video….it can take in audio, but only through the ARC channels.

The Sonos HDMI connection actually works the same as that receiver’s OUT/ARC port.   The difference is that it sends a screen saver video with no sound OUT, not connected sources, while receiving audio from the TV.

Would have been nice if Sonos had added at least one HDMI in in the AMP.

Could have saved a lot of costs when using it for installments as only one HDMI-cable would need to be installed from the tv to the place where the AMP will be located and then all Blu-ray’s etc. could be hooked up to the AMP. 
 

I am building a new house and will be putting in AMPs for tv etc. Due to this limitation, I will need at least two HDMI-cables installed for each tv. 

Then each Sonos device would need to have more than one ‘pass through’ HDMI Port, one for each device you wanted to connect to a TV. And then you’d need to add video switching, too, all of these things increasing the complexity of the device, and the cost of manufacture. And how many pass through ports is the right number? By utilizing the HDMI-ARC system, they’ve allowed the TV to function in all those roles. 

You might want to consider mounting the amps on the wall behind TVs rather than in a central closet somewhere. That would keep you from having to wire hdmi and speaker wires for the amp.  It’s just my opinion, but I don’t think I’d wire blu ray and other sources to a central location either.  For streaming sources, you can use a smart TV or a fire tv/roku stick.  I wouldn’t think you’d need blu ray on every TV, but where you do want it, do you want to have to go to the closet to put in a disk.  Similar for gaming consoles.  Although you may not be using disks anymore, you still need the console to be in range of controllers.

Just my thought, and obviously you may have different needs and goals.  Part of the benefit for using Sonos for whole house audio is that you don’t need to centrally wire everything.

I guess there is no right number, but if they had added just one, I could add more with a switch. 
 

The AMP is directly aimed at installations. It is intended to be mounted in racks for large house installations. In those kind of setups, it makes sense to also hideaway a lot of the devices you would connect to a tv. 
 

And as mentioned, a lot of other amplifiers manage to squeeze several of these in at lower prices than the AMP. 
 

I am not a hater - I am going for the AMP anyway. But would have appreciated just one input. Would have saved me a good deal on installation.

I do indeed. We are going for a very clean look. In-ceiling speakers only. TVs mounted flush against the wall and will be as discrete as we can get  (Frame TV or similar).
 

So will definitely not be putting up cabinets or putting AMPs and Apple TV’s behind the TVs which which will add significant space between the TV and the wall. The Sonos sub will go underneath the sofa. I am ok going to the next room to put in a Blu-ray the few times a year the family lets me dig one out from my treasure chest.

Will have some tiny Alexa devices around the house and a few Apple TV remotes to control everything.

Oh, I completely understand the cost implications for your particular setup. I was looking at it from the company point of view. Is it worth developing and adding a feature that a very small percentage of users might use, and make life more challenging for the majority of their market, which I picture as people not educated in a/v technologies? I would assume some PM/VP looked at those numbers, had a discussion with a group of people, and took the decision that it want the right move for Sonos.

There are a lot of those small decisions that don’t fit my particular world, ranging from Apple, Dell, Google, Sonos, Tesla, Mazda, etc. Not a one of these companies make a product that is perfect for my particular situation, so I make accommodations by picking the one that best fits the needs I have identified. Like both you and I have with Sonos.

There will always be things that we want them to change. We can only hope that at some point, it makes economic sense for Sonos (and the rest of these companies, too!) to do so.

Hi
Without having read every posting, can I use my 4K splitter to carry my TV ARC HDMI audio/ video signals  through my A/V receiver to a second TV in another room ??
Simple solution ?

Hi folks.

@PLGDEES, welcome to the Sonos Community! Can you please elaborate on your concern here? Do you have any Sonos products? 

Just let us know. We and the community are always here to help.

@PLGDEES . Like @Krishma M I really haven't a clue what you are trying tp do but gut feeling is that the answer must be 'no, you can't do that '.