While playing around I beleive I discovered the problem for sounding like your garbled/underwater etc when using Vox.
What is happening is the mic may be picking up the background sounds and sounds of the game. comming through my speakersand mixing with my voice.
I noticed that when I turned the gamesounds down Engine,explosions etc etc.I came through much much clearer.
this woud explain why sometimes I/you can be heard clearly and others times I sound garbled. Thats the good news. the bad news is I had to turn the game sounds down so much that I couldnt hear the game itself other then Vox
Seems the best solution is going to be a headset with earphones.
Unfortunately most headphones tend to give me earaches.
Anyway. if your having problems sounding garbled when trying to use Vox. Try turning the individual game sounds down and see if that helps.
Drediock