This is amazingly useful, thanks for your hard work testing, @FordGuy61! I will try to do similar, time permitting.
My current hypothesis is that the HT-S20R soundbar must be misreporting its capabilities via HDMI. I observe (on a second LG TV now, this one is a C2) that both Chromecast with Google TV and internal Plex WebOS app both have troubles transcoding audio to AC3 with different source materials. I can have smooth playback only if I reencode files to add a copy of the audio track in AC3. Some material refuses to play at all without this manual reencode; symptoms vary from lost surround (PCM 2.0) to infinite spinners to even visual artifacts.
I am also unsure if TV sound settings matter at all – if they could tell both Plex apps something the soundbar fails to (DTV Audio Setting & Digital Sound Output). I don’t think they have any effect, but I haven’t done any rigorous testing.
I suspect my soundbar says it can do PCM without saying it’s only PCM 2.0 (and given @Mojito817’s experience, maybe it’s also confused about AAC?). Given the fact Plex doesn’t offer more granular audio passthrough options, both Android and WebOS apps get stuck under certain circumstances (I have no trouble playing any files using LG Media app via DLNA). Plex apps must be thinking soundbar can do more that it really can (?).
Does anyone know if the are apps (PC, but preferably Mac) that would allow me to connect via HDMI to the soundbar and see what audio capabilities the soundbar is reporting (I don’t know if it’s EDID or what)? Buying any dongles seem excessive.
Lastly, for anyone experiencing similar issues, this is the FFMpeg incantation I came up with (which I use in this very useful app) to automagically add a reencoded AC3 audio track to files. When I do that both Plex apps have zero troubles:
-c copy -map 0:v:0 -map 0:a:0 -c:a:0 ac3 -ac:a:0 6 -b:a:0 384K -map 0:a -map 0:s
