OK, as promised, here are the pictures of my OE CD Changer. The car is a 1998 Omega CDX which had the changer as standard.....
Firstly, here it is installed (I have not taken the original changer out of the car after upgrading to Pioneer Kit):
Next up is the connection at the CD changer - this is the plug that you are looking for in the car:
This is the routing of the loom for the CD changer over the rear offside wheel arch:
You will also need a mounting bracket - this is how mine is fitted:
Finally, for completeness I have pictured the wiring diagram on the back of my changer:
I hope that these pictures help.
However, judging on the post from The Boy, it would seem, as I suspected, that a CCR400 will not control a changer so I doubt if the loom will be present............ In any case, from my experience, you would be better off spending £200 or so and upgrading as I did. Car Audio Security do bundles of Head Units and CD Changers. This is how I got mine and it works a treat. Much better than the standard kit.
Stuart30 - I am afraid that I have never seen an install in an estate. However, as easy access to the changer would be required, I would suspect that it would be much the same as you have described i.e. behind the First Aid Flap.
I hope that this helps.