first, you may want to read the entire thread @ Plex, 4k, transcoding, and you, yes it is long, but contains a lot of questions and answers and wisdom from many users.
second, since your tv cannot play HD (or EAC3/DD+) audio, the audio will be transcoded.
if the audio is transcoding, and you have subtitles enabled, then that can cause video to be transcoded (in order to keep audio/video/subs in sync).
you can switch to an ac3/dd/dts audio track, or change your shield/plex settings to not pass through, so that the shield can decode the audio to PCM so the tv can play it.
this should appear as all direct play on your pms dashboard.
pms > shield decodes audio > sends audio to tv
you won’t get hd audio or truehd/atmos though.
for best results, you really want a 4k/atmos compatible AV receiver or soundbar.
then you should leave shield/plex pass through enabled, and the shield plugged into the AVR/soundbar (NOT the tv).
then it would be
pms > shield > hdmi > AVR > hdmi > tv
and you would get the full 4k + truehd/atmos experience.
