Aftermarket Products to Original Radio's
Found a company called Soundlinx on the internet. They do interfaces to connect Aftermarket Products to the Original Equipment Radio's in the car. They can fit phone kits, CD Changers, iPods, MP3 players, Amplifiers whilst keeping the original Radio. They have a product finder on the website too so its easy to find what fits your car.
Give them a try. I've just had a Sony 6 Disk CD Changer fitted to my Ford Mondeo with Original 6000 Radio.