This should prove easier; these guys are in the UK and provide ready-made solutions for many European cars; there's loads of Rovers too, even if these aren't European but British

These interface directly with Sony so it should all prove to be nice and easy (carefully avoiding the infamous "plug 'n play" words).

Have a look at:

http://www.autoleads.co.uk/product/fitting_kits.asp?action=change&id=30