HDMI-ARC  technically, but yes, that is correct.

No, it’s not normal HDMI, so a splitter won’t work as you’re thinking it will.  You would need a little more complicated, and expensive setup to do it a wired way.  I would probably try using Apple airplay between apple TV and your Amp first.  If that doesn’t work well enough, and your projector has HDMI -ARC (unlikely), then you could maybe manually unplug HDMI wire from TV to projector you need to switch.

If that’s no good, your going to need to look at something like an HD Fury Vrroom or may go with an optical switch.

Think you may be missing one point, or maybe more, I’ve not looked at the Sonance system.

The Amp is looking for an ARC HDMI signal, not just an HDMI signal. So your system needs to be sending the video and audio to the Projector (assuming it has an ARC port) and the Amp is connected to the ARC port on the projector. That will give you a stereo output, with a interpolated center channel, and feed the subwoofer. A second Amp is necessary to drive the surround speakers, but that one will bond wirelessly with the “front” one that has the ARC HDMI cable connected to it.

If, however, your projector doesn’t have the electronics for an ARC output, you’ll need to add a device that has the ability to separate the audio from the video before it hits the projector. If your looking for Atmos, both HD Fury, and Feintech make devices that handle eARC types of connections, or if you’re looking for simple 5.1 Dolby Digital, there are dozens of HDMI switches that have optical outputs on them. 

I believe he got this bundle from Best Buy.  It’s not a home theatre setup, just outdoor speakers running off a single amp.

I didn’t recommend the HD Fury Arcana or Feintech as those are for single sink/display situations.  I think the plan was to be able to switch between a TV and projector.  Since Vrroom is an HDMI matrix, I think it may work ideally for this situation.

@melvimbe You are correct - looking to switch between the TV and projector.

The projector has three HDMI sources, but doesn’t show anything acting as an ARC.

Danny, thanks for the link, it explains a lot. And yes, that system won’t do Dolby Digital, or Atmos, but that’s fine. Your and my posts crossed in the writing, as they often do. 

The OP is still needing, however to get the signal from the TV/Projector’s audio to the Sonos Amp, and there is no “through put” signal for video through the Sonos device, it’s only HDMI ARC input. So 1. won’t work at all. 

The Vrroom, since it has an optical output to support the audio going to the Sonos adapter, while the video is being switched between the two devices, would work. 

The challenge with most HDMI switches is that they work with multiple inputs, and not necessarily switchable outputs, although I admit that I don’t look at them terribly often, so that could be a bad assumption on my part. And it may not be germane whether you have simultaneous outputs or not, since it’s unlikely that one device will be on when the other one is. 

I appreciate all the feedback and suggestions!

I may have solved for this in a lo-fi way.

My projector has a 3.5 audio port on it. I plugged the Apple TV into one of the HDMI ports and then a pair of old school earbuds into the 3.5. Sound and audio were in sync.

So, in theory, I can take an RCA Y Cable, plug that into the 3.5 port of the projector and then in into the analog port of the AMP. At this point, the projector is really no different than a turntable - it’s just an audio device. And given the AMP has auto switching, this shouldn’t be an issue when flipping between devices.

The Amp line-in has a 75ms delay (minimum). The audio buffer is to cater for Sonos grouping across a network and there’s no way to avoid it. So I think you will ‘likely’ encounter lip-sync issues with the video on screen when using this type of line-in connection to the Amp.

The analog line in has a 70 ms delay due to the buffer introduced for multiroom play.  Depending on your sensitivity to lip sync issues, it may not be tolerable.

OK. To level-set. If I go with the Vrroom option. What does that set-up look like?

1 Sonos AMP

1 TV with ARC

1 Apple TV

1 Projector with HDMI (3 ports)

Yea, I misread that part.  You can’t send any audio/video through a Sonos Arc.  It’s an endpoint for audio.

Vrroom is an HDMI matrix with Arcana built in. Pretty sure you would be able to use HDMI-ARC too, although there really isn’t an advantage over optical in this case.  That said, there likely is a cheaper HDMI matrix that has optical output.

I don’t have the Vrroom, but I have it’s predecessor, vertex 2.  Audio out will always match what is sent to the first video output (0).  So unless you plan on having one source to video output (0), and another to output (1)...and want the audio to match what’s sent to (1), then it will work.  Since OP only has Apple TV as a source.  I don’t think other HDMI matrix will be that different.

Apple TV → HDMI matrix 

HDMI matrix → TV and projector via HDMI outputs

HDMI matrix → Amp via HDMI-ARC or optical

The matrix could be a Vrroom or any HDMI matrix with optical output.  Here’s one that would work.

Awesome. Once again - thanks for the guidance! I think this image is what the setup will be.