Here is my first attempt at adding pictures, so hope it goes well. I put in a Kenwood 9980 HD, 2 pairs of Alpine SPX Pro 6.5" with crossovers, 2 kenwood Ampsand 2 MB Quart 12" Subwoofers that are hidden.
The most importiant part for me is to make sure that the constant and
'key on" power sources are directly from the car wiring and not from the exsisting car audio. The Subwoofer power is again a direct power source from you amplifier(s) and not from the BOSE system. The way that I had extra room for the subwoofers way removint the exsisting Audi nav unit and the brackets and the BOSE subwoofer system on the other side. The Amplifiers went in easily and wired them up. If I were to do it over again, I would have placed the crossovers in the doors rather that in the wheel well (and yes, I can still, though barely) get the spare out.
All in all I would say it sounds about 150% better.