The part you're after is the XA-107(assuming your unit's got Unilink changer control). If you want to use it in conjunction with a CD changer, I think you'll probably also need an XA-C30 switching unit.

Info on both at http://www.ice.sony.co.uk/product/allmodels.asp?Category=Accessories&Type=Other

HTH
Dominic

Cambridge Car Audio
http://www.cambscaraudio.co.uk