^ Thank-you for the photos.
Looks like this is the wiring harness for it.
http://www.realoem.com/bmw/showparts...34&hg=65&fg=22
I think the second photo you posted looks like HK amplifier.
http://www.realoem.com/bmw/partgrp.d...70&hg=65&fg=25
Looks far to complicated and certainly beyond me to retrofit unfortunately.