I have purchased a AV Llabs 7:1 Sound System. I also purchased a Sound Blaster Audigy2NX USB. When I play the demonstrator cd the sound is good, comes through all speakers and sub. But when I play music from either a CD or tracks from my PC there is nno sound coming from my sub at all. If I switch the centre speaker jack around with the sub, the sub works but the centre speaker does not. what's going on?? Can anyone help? Baffled!!