Just wondering how you would setup a BFD with a passive sub powered by an external amp with no volume control or gain control? According to the Snapbug guide, you use the processor/receiver sub level control to control the input signal to the BFD and then leave that alone, and match your sub to speakers by the subs volume control. What if it's the above scenario? How do you then control the sub? I'm only asking as I may go down this route with a SVS CSUltra powered by a Nad 216THX amp which has no volume or gain control. What does everyone else think??