Just wondering if anyone can help me with this?

Does the standard X5 stereo (6speaker) run an amplifier? I have installed an alpine amp & 10" sub (in a sealed 20+ ltr enclosure) and all I have to do now is pick up the inputs. I was going to go off the connecters to the rears doors inside the B pillars and run them to the rear (amp has high level inputs) but if anyone know an easier way it would be greatly appreciated. I'm trying to find an easyplace to pick up my input signal.

I'll posts pic's of the sub enclosure/amp mounting when I get the X back from the dealer post the airbag going off in my driveway. By the way, would you believe that they wouldn't even give me a courtesy car whilst mine is being fixed. I even rang BMW Australia and still no joy!

Cheers Matt