I have now got another Sony 6cd changer head unit. The main differences between the two are sound quality and features. I had a chance to play with a 6006e in a focus next to the Sony 6 disc in my car. The 6006 is a cd changer modelled on the same architecture as the 6000cf single unit, only difference is the additional button to load multiple discs.
The Sony adds fade and balance control, digital sound processor for modifying the sound of your music, much improved radio follow when you move from one transmitter to another, smoother gala sound volume adjustment and easier menu system. I also think that the Sony does offer better quality sound next to 6000cd.
The downside if Sony? The disc player is more picky about CDs it plays. I have several that are quite worn and tired from living in cars for years without the best protection. The ford unit plays them fine, the Sony skips over bits it can't play, it kind of self fast forwards.
Other than that, if you have a chance, pick up a Sony. Good quality and any square one will fit any cmax. Straight swap, takes minutes!
2005 Focus C-Max 1.8 Petrol Ghia + Sony 6 disc, 2007 tail lights, Led bulbs all over and HID front fogs.