Anyone here with a Subwoofer setup with the factory headunit? Usually I replace it, but in my 528 I spent the money on an '03 CD53, round to flat pin conversion, and factory AUX in. I could just swap it from one car to the other but then adding a sub is a little different. I'm looking into a line out converter bit I wanted to see if anyone has used a setup like this.

And to clarify, I am looking for MEGA, aftermarket-make-fridgerators-fall, big bass. Ha! Just kidding sorta. Contemplating a single 12 or 15. I had 2 Type R 12s in the trunk of my 325is and I had a pretty slick Type R 8 in my M3 vert. I want just enough to annoy the neighbors but not be impractical for getting groceries.