also, you do not have to have the radio box open for VOX to work.
The best way to test your setup, is to open the radio box, and in the #5 channel, high light it (click and hold down mouse button and drag across all text in that field) and type in your in game name, then hit "enter".
If your sure "t" is the key that is assigned to "transmit", hit "t" and say something then release "t". You should hear what you said from your speakers. If not, you have a problem.