I left AVRs in disgust after the Onkyo 906 overheating debacle decades(!) ago. (I still have the 906, audio only still works ok, for the test bench).
Now I'm running a PC w/7.1 channels, all with top tier (ASR) components, but still using an old 1080i sony projector - and refuse to replace it until the lamp dies (NLA). I too have an old Panny Plasma, but that's not in the music room.
For movies and Blurays I use an older Oppo as surround decoder and analog outputs, to an ADC to USB.
(AppleTV or other streamers use the Oppo's HDMI In.)
I also don't have room for a full size AVR, as my main rack is full, and the AVR system is sqoze into smaller shelves hidden elsewhere.
I use relatively inexpensive center and surrounds and a class AB surround (5 ch) amp - something like $2k all told for the center & surround stuff.
So not quite a top tier input chain for that stuff, but it gets the job done.
I've listened to a number of Apple Music surround tracks, and have not been impressed - clearly not worth it for that alone.
BUT, I host a movie night about once a week with up to 4 visitors, and the relatively plebian audio chain for movies gets rave reviews every time, and of course the 12' 'screen' is a huge hit.
For movies - especially with a projector - this 'medium' quality stuff for audio is perfectly fine (still probably better noise/dyn range than the better AVRs). And a 7.1 system is just perfect for that - my guests still flinch or duck when a 'missile' goes flying by one of the back channels!!
But it's freakin complicated - lots of remotes involved, and the PC has to be rebooted occasionally to 'remember' it's got a USB analog input!
If I were starting over with the electronics, I guess I'd look for a good used AVR that supports as many surround decoders as you want - Atmos is just at the higher/newer end of things.
I'd still use a great ADC->USB to get it all into the PC for sound management capabilities, tho.
For speakers, I'd look hard at the WISA offerings - there finally seem to be more of those coming up. Wiring those things is a royal pain, so I'd at least consider that. (I gave up on waiting for a decent 'surround only' WISA offering, moderately priced.)
BUT, Put your real money in the front channels and subs - most of the Bang! comes from that anyway, and will assure that you have superb 2.1 channel music reproduction.
So use USB devices ("PC" + DACS and amps) which offer a LOT more quality (esp for the money) than any of the AVRs. Dynamic range on the front channels in particular is a major deal - don't skimp on that!
There are many different ways to skin the AV surround cat - and Atmos just raises the cost/benefit barrier.