In the process of selling my A4, I sold my complete stereo system to Nick.  Below are the pics of the installation into his car.  Both sets of door speakers and the rear deck ones swapped easily, as did the install of the subs.  However, the other stuff (headunit, EQ, & the whole trunk side) was new for various reasons (he has a 99.5, where mine was a '00).  Enjoy!