We're talking about two different things. I'm talking about how many discrete objects (channels) are in the source soundtrack. You're talking about how many speakers a processor can derive a signal to feed from that soundtrack.
I explained the limitation on systems beyond 7.1.4. I explained...
Well, Dave Upton enlightened me on this issue. (thanks Dave) I sort of disagree with the term "Locked". Home Atmos is limited to 16 "objects". I believe theatrical Atmos is 128 objects. By default, on all Atmos soundtracks, 12 of those 16 objects are dedicated to the 12 (7.1.4) "Bed"...