It sounds like maybe it's not choosing the audio track that you want? I'd be curious to see the full text output from MediaInfo and/or the XML from Plex/Web. You can get the XML by opening Plex/Web (media manager...), navigating to the video, clicking the info icon in the action bar on the left, and then View XML. Or you can just share [a sample of the file itself](http://forums.plexapp.com/index.php/topic/37215-frequently-asked-questions/?p=393527).
You *may* be able to make it do the right thing by going into the Playback Options and selecting a different audio stream before you hit play.