Stev-A3,
just an update on my solution which I hope will help you. I went for the Xcarlink device from Digibuy. I needed the SKU 143 (£83) with the ISO connector. They actually sent the SKU 1207 but that is the updated one with the sd card, usb and aux which was a bonus.
I used the excellent advice from the forum to remove the radio,glove box and fit the device all in about 1 hour.A big thankyou for the forum members who posted the really useful pics of the installation process
It works superbly well and the 6 cd changer is still available, obviously you cannot see the tracks on the radio but I have organised mine into 5 playlists and used the + or- to move between them. Alternatively you can have it in manual mode and search from the ipod if required.
Hope this helps and let me know if you need anything else.