hi! My friend has a 2005 A6 with MMI Bose and wanted to install some new subs. we have the positive and ground. we just need a remote line and patch level outs. We figured we could tap off of the lines for the rear speakers running from the headunit to the speaker amp in the rear of the car and that amp probably also has a 12v turn on line we could tap off of for the remote line. All I need is the pinout for that speaker amp. Or another way to do it?