The problems with vox arent so much with the sound itself. For the most part, sound quality is an effect of the microphone being used, and wether or not the player is using headphones. (Speakers and a mic will obviously often cause some game sounds to be transmitted)
SOMETHING the game does causes "mic boost" to be invisibly shut off, for no readily apparent reason. It seems to happen mostly on SB Live cards(What else?)
To fix it, go to the windows recording controls, under microphone, go to advanced, turn mic boost off and then back on.
This is a bug.