I have a 3rd generation Amazon Fire TV, and I'm unable to get AC3 5.1 output from the Plex app. All local files and Live TV streams encoded to AC3 5.1 are sent as 2-channel audio to my Yamaha receiver. On the Fire TV itself, I have enabled Dolby Digital over HDMI. Other apps like Netflix properly output AC3 5.1, so the problem seems to be isolated to the Plex app.
Is this a bug with the Plex app? Are there any workarounds to get the Plex app to output AC3 5.1?
This is a major issue for me, since I use the Fire TV for Live TV streaming, which is only broadcast in AC3 5.1.
FireTV, Plex server, and Plex app firmware up up to date as of 1/12/2018.