Thats a theory from 1 guy on that forum who explicitly said "...I could be wrong..." and just "read it somewhere" - probably on Reddit here. Reddit is full of confidently incorrect people.
Plus it's a weird theory since I think Siri in Apple TV is input only. I have never ran into an instance where Siri talked to me from the Apple TV. It will take commands from the remote, iPhone, HomePod etc. I do however have a HomePod, and the HomePod could be taking over the voice feedback. Plus, the Shield has Google Assistant built-in, and obviously no trouble with pass-through, and Google/Android TV software/hardware is hot garbage. I only have a Shield for lossless pass-through. Otherwise it's a buggy POS.
If Apple doesn't implement lossless Atmos pass-through, it's because they dont care about it since 99.9999% of their customer base doesnt care about it.
I'll be the glass-half-full guy, and say that I think awareness of lossless multi-channel audio is getting a bit of traction. Lossless multi-channel is not like the 2 channel lossless vs 320 kbps mp3 debate. In the case of multi-channel, the difference is astoundingly obvious to the laymen with either music or movies.
