Bruce, I'm 99.9% sure that the sub's amp will need to be plugged in. The only way around this would be to open the sub box and see if the amp can be bypassed.

Assuming the sub has both inputs and outputs at speaker level, the high-pass satellite output should function okay, but you'd have to see if the low-pass feeding the sub amp is all speaker-level.

Larry
www.fineelectricco.com