A passive sub is typically driven by both front channels, so I would have been driving it with 180 watts.

Still, a passive subwoofer output is intrinsically tied to the front speaker output and at low levels we were getting almost no bass and certainly no special affect 'hit' in movies, and at high levels it was overtaxing the receiver and ruining the total output. One solution could have been an additional amp, but I don't think the results would have been as good as adding the compact subwoofer.I still have the passive subwoofer in the system but since I have changed the front speaker output to "small", it isn't being driven right now. The sound is night and day between the old setup and the new setup. In fact all channels sound better with the compact in the system.