From what I understand, if you add the 6-disc changer, it sits in the 'storage' space below the main radio, but it does use the main controls, and displays on the MFD. It does *NOT* take over the existing CD slot. (Meaning you have a single CD slot where it is stock, and a 6-disc slot just underneath, hidden behind the smoked plastic door.)
Someone will correct me if my beliefs are wrong, though. (People always try to correct my beliefs.

)