I lost the original subwoofer, the door to the compartment that the subwoofer is now in and the audi head unit(all of which can go right back in very easily when I'm ready to sell the car.

I kept the stock Bose amp/speakers for up front. I didn't lose any controls from the dash that were not part of the stereo. However, with an aftermarket head unit, I now do not have the capability of adjusting the volume from the steering wheel, etc.. And the factory tuner used to show the channel or CD track number in the speedometer computer display... OH well, I can live with that!