Hi, could someone help me with how to hook up two subs from one receiver? My system currently has one sub (PSW12), but my room is large and the bass is not filling well. I want to add a second sub (I have a PSW10), but am not sure how to hook the two up. Should I use a Y cable to connect the sub out on the receiver to the two subs? If so, should I worry about impedance? Thanks.