Below is my thread where I retrofitted a MULF2 HI into an 06 using the TCU wiring. Your current aux wire may go to the head unit so you may need to run a new one to the trunk. If I were to do this mod again, I would just hook a tune2air (bluetooth music) to the MULF2 HI and leave it in the trunk. ebay has some generic standar USB to bmw USB connectors. Aux in is a few new pins added to your TCU wiring.
Most MULF2 HI have the bluetooth phone disabled. In the US, they are normally just used for USB. You may need to enable BT in the module via coding.
https://www.e90post.com/forums/showthread.php?t=1344811