mine didn't have the CDC as standard and fitting one was very straightforward once you have the bits you need
along with the CDC you will also need the D2B optical link cable so you can daisy chain the CDC into the fibre optic loop
each component needs to be connected in a particular order
CD Autochanger
Telephone Module
Voice Module
Navigation Control Module
Power Amplifier
Then back to the Audio Head Unit
ignore the components you don't have
a typical setup on a non premium audio would be CDC , Bluetooth telephone module , SatNav module and they would be linked with the D2B optical cable in that order
your D2B fibre optic cable comes as a pair ( 1 in 1 out ) you need to follow the in and out path of each component to make sure your connecting them in the right order
the plugs on the D2B optic cable can be pulled apart which makes it quite easy modify the overall loop to configure the cable to what you have installed it's just a matter of maintaining the loop from start to finish in the right order
on the wiring loom behind the satnav module you will see a small 3 pin connector which is used to supply power to the cdc unit
good luck...