[jubilex]

Yes, I can confirm this has fixed the delays for me as well, thank you so much! Both with FireTV plugged directly into tv and running through AVR, and both with videos with stereo AAC and stereo PCM.

Now I just need to decide if I can live with no 24fps since the FireTV doesn't seem to play nicely with my Denon in that respect.

Means sometimes you can switch and sometimes not? Might help to shortly switch Input while kodi is in front already.  

I can't ever switch. My AVR has a TV and projector connected, both of which support 24fps, but the Fire TV stays locked to 1080p/60 with no other resolutions/framerates showing as supported in Kodi (also does not switch to 24fps in Plex or any other Fire app). The Fire doesn't ever recognize that 24fps is supported, no matter if one or the other display is removed from the AVR, power cycled, input source switched, etc. No other device plugged into the AVR has this issue and all do 24fps just fine and have for years. It works just fine plugging the Fire directly into the TV of course, but that's not an option for the projector.

I was wondering if something like this might work but I don't know if lack of HDCP will be an issue: amazon link, or maybe one of these: monoprice link