Both Tidal and Apple Music have music in Atmos. I would recommend jazz piano (Oscar Peterson in Atmos, Bob James in Atmos, Bill Charlap, Monk, etc). You happen to have a live piano to compare to. I like to use acoustic piano solo or trios to fine tune the calibration of my settings after running audyssey. Then to test dynamics I really like Big Band and Gordon Goodwin’s Big Phat Band did a nice Atmos mix on the Gordian Knot.
Here is a channel that I think would be perfect for you.
If you get solo piano/trios right and have dynamics like a big band is in your listening room live you can enjoy pretty much anything.