So I think I’ve encountered a bug, and wanted to share in case anyone else sees this (or hopefully someone from Sonos engineering sees it).
If I play Apple Music in Atmos on my Home Theater (ARC+Amp+Sub) I get a nice little Atmos icon in the app showing me I’m listening to spatial music.
If I try to play the same Apple Music track on my Era 300’s (Era 300 Stereo Pair + Sub Mini) I don’t get the same icon.
To troubleshoot I tried to drop the sub, and also unpair the stereo pair, and I still don't get the little icon.
So the next thing I tried was comparing the same track played from another music service (Pandora in this case) to see if there is a noticeable difference. There seemingly was.
So I believe this is a UI bug where the Atmos icon isn’t showing up for the Era 300s versus it being an issue of Atmos not working.