Sorry about this basic question about subwoofers since I've only had a 2-channel system all my life. Is there anyway to incorporate a powered subwoofer into a 2-channel system? I have a 2-channel tuner/preamp with 3 pairs of main outputs for multi-room capability. Can I hook up a subwoofer into a second pair of main outputs or must the preamp specifically have a subwoofer output? Again sorry for this dumb question.