Apple Music Atmos files are all compressed to some extent but I don't imagine that upsets channel balance/imaging much if at all? Some time back I compared a couple Apple streamed versions against my BluRay versions and didn't hear any major distortions but it's very hard to set up streaming for any kind of serious A-B tests.BTW, I have no idea what, if any, transformations are involved in going from the discrete 5.1/7.1 HiRes stuff I download from them to the Atmos packages on ATV.
I have the 19 cut 2L downloaded 5.1 sampler from 2009 but I don't believe its in Atmos on the stream?
Just a bit of curiosity. LOL