There are now hundreds of Dolby Atmos remixes of classic stereo recordings. It’s not generally understood that Atmos is a superset of Dolby Digital 5.1, and Atmos content will be automatically down mixed with no loss of fidelity to 5.1 if the AVR does not support Atmos.
My setup is: AppleTV 4K -> HDMI -> Marantz AV8003 pre/pro -> Marantz MM8003 power amp -> 5.1 speakers. This receiver dates back to 2010, long before Atmos, but the AppleTV automatically sends discrete, uncompressed 5.1 channel PCM to the AVR. Sure enough, the Atmos mixes play back perfectly in 5.1 surround, and are quite different than the 2-channel mixes. And there are hundreds of titles in Apple Music in Atmos format ... some new, some going back to the late Sixties, like The Doors.
True, the quality of the mixes vary, as it always has for surround sound. Some are very much better than the stereo release, and others are gimmicky and not very good. But most are an improvement on the stereo version, which are only a few clicks away if you prefer that.
Apple Music lets you choose tracks in several formats: 44.1/16 CD resolution in stereo, 96/24 resolution in stereo, and Dolby Atmos, which appears on the faceplate of the receiver as 5.1 PCM Discrete (not Dolby Digital). Based on the display, it is the AppleTV, not the receiver, that is decoding the Atmos stream and converting it to uncompressed PCM streams.