I discovered today Apple Music Atmos music tracks downgrade to non-Atmos when at least one non-Amos speaker or set is added to the playing group.
The tracks John Coltrane's Blue Train played in Atmos when grouping an Arc + Era 300 surround set, Era 300 stereo pair, and Beam Gen 2 + Sonos One surround set.
When I then grouped a Sonos One stereo pair the music dropped very briefly, the Atmos logo disappeared from the Sonos app Now Playing screen, and the music resumed in stereo. The difference was definitely audible and a downgrade.
It's disappointing to have to downgrade to the lowest common denominator if I want to have music playing throughout my home.
I'm going to read through the iTunes Package Format documentation, not sure if it will provide any insight. What's weird to me is Atmos music will play in my Beam Gen 2 + Sonos One surround set, which includes two non-Atmos speakers. This gives me some fleeting hope Sonos may be able to address this limitation via a software update.
Have others seen this? Any idea whether it's an Apple Music, Sonos, or recording-specific behavior?