Subtitles aren't working from iTunes

Hi All,
Ive unlocked iTunes movies using a DMV stripper/remover (TunesKit) and the company who i bought this software off says that it can bring subtitles across from iTunes - I have even called the creator of the software and they say it works (however they don't know why it doesn't work on Plex). It has successfully done this when i play the movies on quicktime but after that when I want to upload to Plex they don't work/show up even when I select the language I want. Does anyone have a fix or know why this isn't working?
Thanks!~