I have a factory (not the bose) premium system. On the back of the factory radio, there is a 2 pin connector. The pins are marked SUB and MAIN. Does anyone know what this is for? I assume it for the connection of the Bose sub. If so, I would like to know what signals are on these two pins. I would like to see if I can run these to an amp and run an after market sub right off the radio. Any Ideas?