How is the best way to tap into the mach 460 stereo on an 03 Cobra for a subwoofer amplifier. I have a line level converter by scosche. I saw someone post on one of the websites (forgot which one) that they used the incoming wires to the factory amp, black/green stripe, black/white stripe. I tried this with the line level converter and it does not work. Is this a low level input that I should just solder my RCA cables to directly? Help!!!