We just bought a new home and it was pre-wired for surround sound. I had no problems hooking up the center channel and surround sound speakers, but I'm having difficulty setting up the sub. I have a Onkyo TX-SR504 amplifer with a lone RCA pre-out for the sub. I have a Speakercraft BassX 10 that has it's own amplifier and RCA inputs. Problem here is that the wires in-between are speaker wires with four different colors. There are actually two different sets of wires, one with 4 wires and one with 2. I know it's probably easy but I'm a bit befuddled. How do I get convert the four speaker wires to RCA plugs to connect the amp and the sub? Are their adapters for that? Thanks in advance.