If you are, or think you might in the future, start collecting 4k/uhd/hdr content, then you should read this entire thread @ Plex, 4k, transcoding, and you
the long and short of it is, not all 4k clients are created equal, some work much better than others.
HD audio is a constant problem for anyone without an nvidia shield and an atmos receiver.
Subtitles are another common problem, different clients have different subtitle compatibility
Incompatible subtitles + incompatible (HD) audio = transcoding.