It's interesting that you're so negative toward Plex and XBMC. My brother and a friend of his use XBMC with zero issues (even their wives, who aren't terribly computer literate, have no problems using it), and they've not run into any media it won't play. I have similar experience with Plex (and have been trying to get them to convert).
In my case, I've only thrown .mkv files at Plex, since that's the container all the pirates seem to use for movies (I have no idea why, and I've not bothered to look into it). I've never had issues with playback on my HTPC (which has Plex Home Theater), my phone and tablet, both of which have the Android Plex app, or to my work PC via the Plex Media Server web interface. It even supports subtitles, if their built into the file (I've never tried downloading/adding them manually, so I don't know 1) if it works and 2) how difficult a process it is).
What kind of problems have you had with Plex (don't worry -- beyond being a user, I'm not affiliated with the company -- I'm just curious)?