Maybe it's just my case but having a domestic wired system with a Shield Pro as media player and a QNAP 653A for data storage, I honestly was aspecting better performances in terms of quality while running Plex.
I have several 1:1 BD mkv and in some cases the playback is not fluid, often getting stuck or slowed down. Running subtitles is a nightmare, both pgs or external srt, I tried all available options but nothing change. Audio as well sometimes appears turned down. I tried running the PMS both on NAS and Shield but nothing really changed.
Please forgive me if I say it, but playing files with Kodi, but also VLC, is completely another story. So far I haven't detect any issue faced with Plex.
Did you also have this kind of problems and eventually find a solution? I honestly would like to continue to use Plex since I love the way it is built.