I'm actually pretty savvy at this audio stuff, but for situations like the Beatles Abbey Road Super Deluxe Edition, I'm stumped.
There's a genuine 5.1 (non-Atmos) mix of this album (I own it). But are we getting a stereo version of "Here Comes The Sun" that has matrixed Atmos that decodes the 2.0 signal? There's no discrete 5.1 + Atmos music available via Apple Music, right?
Quoting myself here, because with a bit of experimentation, I did find out the answer to the above situation, I hope it helps others.
With Atmos tracks, you
are getting a real, discrete bit-stream, lossless version of the track, via AppleTV 4K. Essentially the same you get from recent BD/4K UHD material.
This is great news, all around
And I consider it the final death knell for the "legacy" hi-res surround formats from the early 00's - SACD and DVD-A (I own hundreds). We now have support from Apple, devices in millions of homes, and content that you get by pressing a button. No going to the store to find a disc, no backwards compatibility issues.