Further research is pointing to buying a Resler interface and using Navcoder as KiwiJochen says....
Is the Resler interface easy to hook up? Is it just a case of unplugging the CD changer, plug in the interface and then use NavCoder to change the unit to colour rather than Monochrome?
Also - is there anyone around the Thames Valley area that has Navcoder and a Resler interface
Thanks again guys - pretty steep learning curve on this one!
Chris