I am trying to add a subwoofer to my system, which includes a Sony 835 digital reciever and a Bose AM-6 speaker system. I have a powered sub that has two RCA plug inputs on the back, labeled left and right. The back of my reciever has two plugs for the subwoofer out, but they're not labeled L and R. I believe these are for two separate subs. So I tried hooking up just a single RCA plug from one of the sub-outs on the reciever to one of the RCA ins on the sub. However this is not working. I also told my reviever that I am using a sub now, so what else could it be?