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

Have you contacted Apple about this?

Since every other app works though the Apple TV, why do you believe this is a Sonos issue?

I get that users have lost some trust in Sonos because of the issues associated with the new app launch, but Sonos products only play whatever format it is presented with.

As I understand it OP’s disappointment lies in the fact that stereo sound from a TV source does not play over his surrounds. This has been asked to ad as a feature for a long time - especially because this has never been a feature. I do not think that OP is right when he states “It worked fine before for atmos or any other format.”

I can write a very long response to this, but lets just say I disagree with stereo from surrounds. 

When you go to  live performance, do you turn your back to the stage, or do you face the stage?

I just feel that, it should be the same inside your home.

To leave out personal preferences I think there are people who like surround sound for musik and others don’t. Imo the „problem“ is that Sonos makes no difference in tv mode between tv stereo content stereo and music stereo content.

I think the solution could be to add an option like many classic avr devices do. Give the user an option for tv mode stereo signal to select between dynamic DSP result or fixed full stereo signal also for the rear speakers. This also would make users happy who like classic spoken tv stereo sound also on their rear speakers. 
​@106rallye … I think OP was talking about playing Dolby Atmos music in tv mode or watching a concert with DD5.1 audio track when saying „it worked before“. For stereo tracks in tv mode it always was the same like now. Just the results of automatic DSP surround simulation sometimes are quite different depending on the source stereo track. 

Try turning Continuous Audio Connection off in the ATV 4K audio settings. It is new as of a few tvOS updates ago (tvOS 26.4). That setting sends all audio out in Dolby MAT and might be the reason you hear a difference. I have mine turned off as I didn’t have any of the problems that new setting is supposed to fix and didn’t like the way it sounded.

Interesting… I‘m pretty sure that this function doesn’t have any effect on the audio output you will hear. For my understanding it just put it into another format. 
Just speaking for myself I didn’t hear any difference when turning it on. 

With it on, all audio is sent in Dolby MAT (which Sonos displays as Atmos, even when it’s not Atmos). According to Apple, it is populating the correct channels within the Dolby MAT for the content being played (the remaining channels being silent). It just doesn’t sound right to me. Sonos no longer does the processing it would normally do for stereo 2 channel audio.

If you have an amp that does surround processing on stereo 2 channel audio, that will no longer work with the Continuous Audio set on.

​@kdowling 

I never noticed that… maybe because I tested the option just for some hours and decided not to use it. So the normally simulated rear signals the DSP creates from a stereo signal in tv mode won’t be there with the option turned on!? Did I get it right?

That is the way I understand it and the way it appears to work here. Since the ATV is sending silence on the channels not used, instead of just not sending them, the receiver/amp/soundbar is going to play silence on those channels.

The following assumes that surrounds have been set to Full for music which automatically increases the volume/presence.

Apple Music plays through my Era 300 surrounds with Arc Ultra sound bar. However, the surrounds are not as loud when streaming music through the app. You can adjust the volume level of surrounds. Another trick is to set the distance as 10 feet or more if not already set as such. Doing so causes the surrounds to play slightly louder. 

Regarding Continuous Audio. I find that leaving it on expands the sound stage of the Arc Ultra. I did an A/B test while playing the same track and the presence was much improved with Continuous Audio set to on. That said everyone’s listening experience is difference.

One more thing when playing music via the TV. Click on Speech Enhancement and you’ll see that it is recommended to be turned off.