Audi Repair: Radio is locked, audi radios, gamma cc

Question
Hello Jan thank you for your time.  I recently bought a used 1995 Audi A6 and placed an aftermarket radio in the car.  It worked alright but I do not like the way it sounds so I wanted to put the stock radio back in.  When I went to do so it locked up and i am unable to use it. I hope that maybe you have an unlock code that I would be able to use.
The unit is a balupunkt Audi gamma CC Serial number 7 640 859 380 AUZ1Z6B0107708.  There is also another set of numbers 4A0 035 093.  Once again I am very grateful for your time on this matter.

Answer
The code is something which is entered after purchase, so there is no way of me knowing the code.  You can look in the documentation that you have with the car for a four digit code.  You can also take a look at: http://www.ibiblio.org/tkan/audi/radios/  for info on the radio code entry, but you will need to get the code from an Audi dealer, or you may be able to find it on line.  Let me know how you get on,  Jan