This isn't the most simple case. You have the AGW unit in the trunk and all speaker wiring comes from that unit (since it is the amplifier too).
If it is an NTG2.5 COMAND that you are after (this was not present since the introduction of the facelift but from some 07/2008 or so onwards).
Many forum members have done it but you would need a wiring harness from the front to the back (kabeldaviko or comandonline) and some other changes. The radio antenna amplifier is not exactly compatible and the hands free microphone neither.