Please follow up if you find a resolution to this. While I can address my height channels using the Dolby Atmos Renderer when mixing, I really need to be able to play reference Atmos mixes from Apple Music or Blu-Ray (once MacGo updates) and need a better pipeline than doing an external decode of aTV output with a receiver and capture of 12 channels via an audio interface.
I've noted that Apple Music "Atmos" only feeds 5.1 channels of a 7.1 setup so far, on Big Sur.