If the sound output on the Now Playing Screen says Dolby Atmos when you’re playing Atmos content on the TV, then you’re all set. Also make sure any Dolby Atmos output options are set to on in your TV settings menus. 

If you have Apple Music set up as a music service on Sonos, you can always search for ‘Dolby Labs’ and play some of their 7.1.4 tracks to test you’re hearing it all. 

And if you don’t trust the “Dolby Atmos” label on the Now Playing screen (do trust it), you can download Dolby Test tones for Atmos here:

https://www.demolandia.net/cinema/dolby-demo-trailers-hd/page-10.html

Download them onto a USB stick and play from your TV, or send them to your streamer. 

When I try to play the Dolby Labs tracks, I am still receiving the ‘To get the full Dolby Experience...’ message.  I am playing Apple Music as a service through sonos, and have my appletv plugged into sonos eARC.  In the sound settings for AppleTv I have Atmos enabled.

How are you playing the Dolby Labs downloads?  To eliminate anything else, I would download them to a USB stick and connect them directly to the TV.  When I do this, I get each tone coming out of the correct channel (L-C-R Front, L-R Surround, L-R Atmos Height, Sub). 

I added Apple Music as a service through the Sonos app on my iphone.  I understand that playing the files via apple music doesn’t work, but playing it through the Sonos app is supposed to work.  I have the AppleTV running through an HDFury Arcana to my projector, so I don’t have a way to test via an mp3 stick.  All speakers are working, and the audio settingn on AppleTV say Atmos available, I just want to make sure the atmos is actually enabled and functioning, and haven’t found a definitive way to do that.

I’m not familiar with Apple TV, but without a way to play those test tones, you need to assume the Atmos icon on the Sonos app is a definitive test. 

Not seeing that, either.  That is what made me start looking for other testing methods.  Is there any reason that an Arc, Sub gen 3 and two Era 300s, showing up as surrounds in the app, would not be atmos ready?  I wasn’t sure if something weird might have happened and I needed to reset them and start over.

It all depends on the settings on your TV and streamer (Apple TV seems to handle Atmos very different from other devices).  However, if you are playing Atmos Audio from Apple Music using the Sonos app, you should be seeing the Atmos logo on the Now Playing screen.  See below:

Thank you for your help.  I will try again and see if I am seeing the logo. Is that the newest version of the app?

Yes.  But it has been that way since the release last month.  Make sure you are playing an Atmos track.  Search for Spatial Audio, and there are several playlists featuring Spatial Audio:

Awesome.  Thank you for your help.  I will give that try this evening.

Apple Music through Sonos app wasn’t playing Atmos.  The newer version of the app fixed that.  All is good now.