You and I may be comparing two different things. I don’t have an Apple TV4K, which Apple says is necessary to get at the version of Dolby Atmos on Apple Music that’s needed to feed an outboard Dolby Atmos processor. From my iPhone, iPad and Mac Mini I can only get access to a 2-channel mix that is designed for 2-channel listening, with no mwention made about any further decoding to feed 7.1.4 channels, or what have you.
Well that explains a lot. You are not going to get proper atmos without an Apple TV4K and external processing. Whatever Apple is doing for headphones with their built in processor is definitely going to sound wrong on speakers.