eric,

one of my cars is also a passat (1991, stil runs very good with 140K miles) and i have a similiar 'seam'. i ran mine up thru the bottom panel under the steering wheel (couple of screws gets it open) and voila!

on another post, i have also suggested taking it to a car radio installation shop.. they will do a great job for little or nothing in price.. thats if your car is not a user friendly as others.....