The most complex Atmos system you can build is 24.1.10 so that’s 35 audio output channels. Sure the audio is packed on disc in 12-16 channels. But Atmos is object based, the Atmos receiver can calculate where the sound should play across those 35 output channels.
I was aware that there was algorithmic expansion that could be done, but I did think it was a maximum of 12 real channels (L, C, R, SL, SR, RL, RR, sub, 4x overheads)
What are the other 4? Do they add channels between the ear height and overheads?
Full fat cinema atmos can scale to (iirc) 512 channels. (Things may have changed since I last was involved!)
In that case, it's a 7.1 bed, and all the other channels are effectively coordinates in the room, and the processor steers objects between them in real time, rather than having defined tracks.
I think those are purely object based channels that a TrueHD receiver can’t use. So that’s for audio sources that will be added across the other channels and subtract where necessary to remove duplicate sounds.