Sorry if this has come a bit late, but it may help others!
For anyone else doing the Dension install it is far easier to simply take the most connector apart in the back of the head unit and connect the most cables there, and then crimp the 12v and ground to the same connector.
You can then tuck the unit down behind the trim in the passenger footwell.
This takes around 20 minutes including running the cable to the centre console and the aux/service switch to the glove box.
My local Autologic dealer charges 30 mins for coding the Dension, used to code for CD changer, they have now added a button that says 'Dension' so the garages who don't know anything about it can't go wrong.
30 mins at my garage is £32, so around $45.
The car does not have to be updated to take the CD changer either, BMW will try and tell you they need to update the whole car, this a BS, it is just BMW AG using it as an excuse to update it and charge you for something you don't need or even want.