apple tv 4k theater set up: arc ultra era 300’s gen 3 sub

I think you may be mixing up two different things. The “Full” setting for Music Playback on surrounds pertains to playing music via sonos. It has nothing to do with audio coming from the ATV device. Which is TV audio via hdmi. The Continuous Audio Connection setting only applies to audio from the ATV device. Doesn’t matter if it’s music or a movie. That is what is being discussed. Apple Music on ATV to TV to Sonos. If the music you are playing from the ATV is 2 channel stereo, the sound will change depending on CAC being on or off.

Edit to add: My testing has been with Beam 2, Sub (Gen 3) and Era 100s surrounds. 

It’s a misnomer in labeling. It has more to do with inputs (‘streaming’ versus ‘from the TV’…not really sure how to label that, since it could be HDMI or optical input…perhaps why it isn’t easily labeled in the controller). Music itself can certainly come from ‘the TV’. So it gets confusing. 

And, not to put too fine a point on it, if Sonos ever moves from direct input from the TV sets to streaming across some other method, it will be even harder to simply identify these differences…so that your mother can understand.
 

Which, I think, is still the ‘ease of use’ Sonos is striving for. Satisfy the larger ‘ease of use’ crowd, rather than edging into the perceived ‘audiophile’ smaller audience. 

I don’t believe I’m misunderstanding anything. The OP said his surrounds are not putting out (any) sound when playing music via AppleTV. I did my investigation using ATV via my setup. My response was that The surrounds are not as robust as opposed to streaming but there is audio.

My intended communication to the OP was to make sure the  surrounds were set to Full. They could also adjust the volume and or play with the distance setting which I did as part of my testing. Failing all that I would think the OP would run a diagnostic and contact Sonos Tech support.

So unless the OP completely misstated (worded) the issue I responded to what was submitted. I didn’t try to speculate what the OP may have meant nor detract from their post.

The comments about Continuous Audio setting was in response to another member interjecting that aspect  into the conversation which the OP didn’t mention. I merely gave my opinion on the use of Continuous Audio.

Lol. Ok.  Let me rephrase... The OP is using an Apple TV 4k to play “Apple Music through the tv”. The Music Playback surround setting of Ambient or Full does not effect tv sound (hdmi soundbar input).

I am the other member that interjected CAC into the conversation. I’m not going to re-explain why. The OP can test and see if it fixes their problem of no sound from the surrounds when playing Apple Music through the tv. If not, they can turn it back on.

Way back, further than my memory is reliable, didn't someone Sonos say something about a soundbar generating ambient rear channels when the TV is sending a stereo source?

Who knows how many firmware revisions back that was, even if I'm recalling correctly?

Too many other pots on the fire today to fool with it and I don't have Apple TV anyway.

Yes, exactly. But that is not related to the Ambient/Full music playback setting.

If CAC is on and the Apple TV 4K is sending silent rear surround channels (all channels silent except left/right) for a stereo 2 channel audio, sonos is going to play silent rear surround channels. ie, silence in the surrounds. So instead of playing the ambient rear channels it would normally play, you get nothing.

Edit: This is what I meant above when I said “Sonos no longer does the processing it would normally do for stereo 2 channel audio.” It also effects center/sub.

I’m not going to say anymore on this subject. However the AI generated synopsis below gives a good explanation. Whelther one indulges or discards everything by AI is a personal preference. Take from it what you will.

I’m not sure what any of that has to do with what is being discussed here. No one has mentioned anything about using Apple Music on iOS/iPadOS/macOS. Nor has anyone compared Apple Music on those devices to using Apple Music on an Apple TV device. I’m completely confused on what your point is, so I’m out.

When I first purchased the arc ultra I quite often use the music app on Apple TV and played atmos and stereo audio through my theater. It produced a full soundstage and responded to ambient and full playback selections in the Sonos app. 
 

Now only when using the Apple TV Music app the surrounds are not producing sound for any type of audio. 
 

Even if this is an Apple quirk a company like Sonos should have known about Apple updates before they happened. Or the very least have explained why they don’t support Apple Music on Apple TV. 
 

rebuilding the theater group from factory is what I need to do to test this further. (Another thing Sonos should not require so often)