Thanks Und. That makes sense in this context that the subwoofer requires amplified power. It's confusing since in an electronic sense the term passive is used for speakers that never get power. They just set there and virate. In this case it still requires power but from and external amplifier and the reciever only provides low level line outputs. The sell cheap single channel power amps. With shipping the cost goes up but a local store might have some like Radio Shack.