Checking the Trunk end of the connection ..... The Antenna cable used for the old CPT 9000 phone terminates in the trunk to a Male Fakra in my 04 M3. In order for it to be connected to the BT/Assist TCU (for the handset in the cradle to take advantage of the external antenna) you would need a Female Fakra to Female Fakra adapter cable !!

I would imagine this will be the same as your 04 as well !! You could ofcourse connect the female Fakra connector from the external antenna, directly to the male Fakra connector of the cradle antenna cable, however if you did this, now the TCU would not have a antenna connection ... which would mean Assist would not be able to make calls !! :-) So it would be best to try and find the adapter cable I mention above.