Your Apple TV needs to connect to the TV through a non-ARC port, and the Arc will connect to the HDMI-ARC port.  ARC stands for Audio Return Channel...the TV is responsible for sending the audio from HTML sources (Apple TV) and it’s internal streaming apps through the ARC port to your Arc.  Your Amp won’t be connected to anything, as it can receive the rear surround channel audio from the Arc wirelessly.

Your 5 other amps can’t be used for this TV room.  They can be grouped with your TV room to play music in sync, and play TV audio with a slight delay, but they cannot play specific audio channels for your home theatre.

Also, In order to get an Atmos from your AppleTV, through your TV, to the Arc, your TV has to be able to take the signal it gets from the AppleTV and convert it to a dolby digital + signal that can be passed through the ARC to the Sonos Arc. 

Note, some apps (non Apple apps like Netflix, etc) in the Apple TV will already send Atmos via Dolby Digital Plus. The Apple apps are the only ones that you may need to be concerned about your TV being able to translate. The format being sent (Dolby Digital Plus versus MAT/TrueHD) are determined by the source playing on the device, and not the device itself.

Too incredibly helpful answers - THANKS.  Couple of what may be silly questions.

1. melvimbe, can you please expand on “Your Amp won’t be connected to anything, as it can receive the rear surround channel audio from the Arc wirelessly.”?  My Amps are all connected via ethernet to my router.  Would it be helpful to connect the Arc to that Amp using the extra ethernet port?  May be unnecessary but I tend to lean wired if possible.
2. I currently have a subwoofer (not Sonos) connected to the Sonos amp that will ultimately be the amp that powers my rear/surround speakers.  I read that I won't be able to use that Amp to power the rear/surround speakers AND the sub.  Q: Since I have 5 other Amps in the same closet, any suggestions of how I could continue to use that (non Sonos) sub?

Thanks to you both, melvimbe and Airgetlam!

My apologies on this.  I was trying to keep in simple by stating that wireless connection is the way to go, but you can use ethernet wiring instead.  If your amp is not in the same room as your Arc, in central location or basement perhaps, then it would be helpful to have a wired connection between the Arc and the Amp running the rear speakers.  That connection can be director it can be indirect with both devices connected to a router or switch.  Basically, if there is a wired path between the Arc and your Amp, the devices will communicate through that path.

What you read is correct.  The sub port on your Amp is turned off when the amp is handling surround sound duties.  Could you connect the sub to a different amp in a different room?  I am guessing that  might not be doable if you’ve already done wiring in walls for the sub?

Thanks again!  All of my Amps, Arc, and non Sonos sub are in the same spot (cabinet holding my living room TV).  Was thinking I could plug the sub into another Amp, and when watching TV, group the sub Amp along with the Amp with the rear surrounds and the Arc.  Seems like a lot of hoops to jump through however.  But I can't think of another route to connect the sub (without buying a new, dedicated Amp… or Sonos Amp).

There’s no way to add a third party subwoofer to an Arc based system. You would have to use a Sonos Amp with any Sonos sound bar. The only way you can use a third party subwoofer in a Sonos home theater setup is if you’re using the Sonos Amp to drives pair of front speakers with the faux center speaker. 

Thanks again Airgetlam - so it sounds like using one of my other Amps and grouping would actually work?

Not unless you gave up on using the Arc and Dolby Atmos. You can use a non Sonos subwoofer only when using the Sonos Amp to drive a pair of your own front speakers. That’s the only use case when there is an active subwoofer output. 

When you group rooms together, the audio is automatically delay to allow for proper syncing of multiroom audio.  So when watching TV, the Arc and rears would play in sync with the TV, while the sub (grouped from a different room) would be delayed, creating an echo effect.  As well, your Arc will not act as if a sub is present, and will continue to play the bass notes.  With a Sonos sub, the Arc will leave bass notes to the sub and perform mid and higher range notes only.

FYI, you never notice the audio delay when playing a music source.  Because there is no TV video to match to, all audio is delayed and you never really notice.  It really only becomes a factor with TV audio.  For wirelese speakers in the same room playing TV, Sonos uses 5.0 Ghz wireless for communication over the shorter range and with delay that really isn’t noticable.   I know that you are not using wireless for your situation, but the principle and operation of the system is the same.

Ah, thanks again guys - very helpful!!!

I know this is getting into tech territory, but couldn’t you put a dummy load on the speaker outputs of one of the AMPs and use the SW output and then group that AMP together with the ARC ?

You could do that for music playback, but with TV audio, speakers in another room, grouped, are going to be delayed aroun 70ms.  Your bass will be slightly behind everything else.

All these responses are great! Like the OP, I too have been searching for a better explanation of how the Sonos Amps and Arcs are supposed to integrate with the Sonos family.

To achieve a more discrete setup, is it possible to use the Sonos Arc as a dedicated center channel? Then use 2 Sonos Amps to power 2 discrete pairs of in-wall speakers? (One set for the Front Left/Right and another for Rear Left/Right speakers? Finally, a Sonos Sub would be wirelessly paired with either the Arc or the Amp?

Separately, are the in-ceiling speakers an upgrade over using the Arc alone?

Looking for a similar situation. Have a pair of ceiling and rear speakers to connect to a Sonos setup. 
 

Planning to get an arc and sub playing audio from the tv hdmi-arc port on the tv. 
 

Question is if I can create a home theater set up with an ARC and sub, along with 1-2 AMP units connected to the rear and ceiling speakers? Or will that be it synced?

Thanks for the help!

A home theater set up with an Arc can only be connected to one Amp (for surrounds). Depending on the load the ceiling speakers put on the Amp, you could connect all four speakers to the Amp, but they will put out surround (rear) sound. If you’d use two Amps, one would not be part of the home theatre set up and lag behind when grouped with the HT set up.