I recently bought the Mirage MX 5.1 home theatre system. It sounds terrific overall except the subwoofer is working at minimal volume. It has two RCA jacks on the back of it, one L and one R. On my Denon reciever, it has a single subwoofer jack and a L and R jack as well. When I plug in the sub with a single cable, the sound is very weak. I tried using two separate cables to connect the L and R on the receiver with L and R on the subwoofer, but to no avail. What am I missing? Do I need a Y cable?

Luckily, I had an old Mirage subwoofer with a single port that I plugged into the single port on the Denon receiver and I have full-range subwoofer capabilities as a result, but I'd like to figure out why the MX subwoofer isn't working properly. Thanks.