I've taken out a Stock hu out my Audi A3 1.6se ( bose sound system sub and amp in the boot side quarter , powering back and sub woofer )
the headunit takes 4 din plugs and one aerial, the 1 din is for front speakers, 2nd for power, etc, 3rd din is for line out 1& 2 + remote wire ( immitatend RCA ), 4rd is for dimmer lights....
Taken 3 pics for you, to let you understand it better.
One is the headunit head on.
[attachmentid=625]
Second is a diagram of the din plugs
[attachmentid=623]
third is the din plugs them selves
[attachmentid=624]
Hope that helps you]