Concert 2 (Half Amp or BOSE)
The single DIN Audi Concert II head unit was either rear amplified or fully BOSE amplified. If you are unsure which you are, you can remove the stock radio and check the ISO speaker block on the vehicle side. If there is only 4 pins pinned out of the 8 pin slots, then you have the rear amplified system. If there is no pins in the speaker ISO block, then it is fully amplified.