[Darren]

I guess you would need the antenna - but whats the point if the sat-nav disc isnt available? The Nav unit is nice and looks the part - you would need a double DIN aftermarket unit if you wanted to replace what you have stock which will be equally difficult to wire up - especially if you want to retain steering wheel controls etc (bear in mind that many of the aftermarket Nav units the guys is the states are fitting are able to support the GM interface - I doubt you will find a system that is UK nav compatible that will be available with GM USA steering wheel control interface).

Let us know if you find out whether your contact in Germany has a functioning factory fit nav unit and if so where he got the disc (I'm guessing off a vette or caddy?)