HBO Max won't serve Atmos audio on TCL Roku TV Series 6
I've got a TCL Roku TV 55R635 running audio through a new Onkyo receiver (using eARC). Works like a dream for the most part but the HBO Max app just won't serve me Atmos audio (or Dolby audio of any kind, for that matter)—all I get is PCM, even on Atmos content. Netflix, Apple TV, etc. all send Atmos audio to the receiver no problem (I've got audio set to "passthrough" and the TV is detecting that the receiver supports DTS and Atmos). And just for fun, I hooked a Roku 4K Express from the other room to my receiver, and the HBO app gave me Atmos audio on there—so it seems to be a problem specifically with the HBO app on the TCL TV. Anyone else come across this problem and have any ideas?
TLDR:
Other TCL Roku TV apps + my receiver via eARC = Atmos
HBO on another Roku + my receiver = Atmos
HBO on the TCL Roku TV + my receiver via eARC = PCM
(Another weird thing is that the HBO app only gives me HDR on their UHD stuff, not Dolby Vision—again, other apps that promise Dolby Vision give it to me no problem. But this is obviously less of an issue than **bleep** PCM audio to go with my nice 4K picture.)