[sirmedia]

It depends what you mean by everything. I'm having problems with DTS and AAC 7.1, DD/DD+ seem OK.
You should also check that sound actually comes out of all speakers, don't rely only on what the AVR reports, it may get multichannel but surrounds could actually be silent.

By "everything" I meant everything, including DD, DTS, TrueHD, DTSMA, and AAC, and sound is indeed coming from all speakers. Yesterday, I even tried to induce the problem by changing Kodi from "Fixed output" to passthrough, and I couldn't get anything to transcode to DD. That which didn't pass through was output as 7.1 PCM.

You're lucky. Don't touch anything