Audio Systems: swapping becker head unit, land rover discovery, impossible cd

Question
I have an 03 Land Rover Discovery I want to swap the head unit for a Becker sat/nav unit which is also a OEM install on some units.  I have swapped them, but the sat nav doesn't seem to work/ says error, the volume, mode control on the steering wheel doesn't work and the CD changer doesn't work.  Am I looking to do the impossible?

Answer
cd changer is not going to work because they are not the same
steering wheel controls are on a different plug ( top left plug behind the radio ) it will need to hard wire
the only reason the nav is not working is because of the antenna  is missing or it needs the speed sensor wire from the vehicle
this cable is not in the original radio plug

good luck