The factory Audi stereo is fair at best. The Bose upgrade
from the factory is marginally better than stock. It's an OK
solution if you are not a serious audio enthusiast, but I desired
something more. I have the 99 style head unit, so the radio head
unit is normal Euro-din fit, not the weird huge unit that is found in
The biggest obstacle I had initially was trying to figure out where
I was going to run my 4 gauge wire from the battery to the
amplifiers in the trunk. I looked for a hole from the engine
bay through the fire wall but eventually resorted to running the
wire through the grommet where the hood release cable runs through.
I just ran some extra silicone around the grommet so no water would
leak into the car.
The front speakers -- I replaced
the front speakers with MB Quart's 5.25" separates. If you get the MB
Quart adapter for the front speakers, it makes life real easy. The stock
front speakers are only 4" big so the adapter is necessary to make it work.
There is a crossover box included with the front speakers. I placed it
between the door and the foam insulation right above the power window support
bar. It will be obvious once you have the front door apart.
The rear doors -- I added speakers to rear doors. The door panel is the same with a Bose setup or without a Bose setup, except on the non-Bose setup the speaker grille and hole for the speaker is not there. I ordered Bose speaker grilles and cut the whole for the speaker with a Dremel tool. To get a 6.5" speaker to work I had to get an adapter that extended the rim around the speaker so I could screw it into the speaker posts. The only problem I encountered is that an MB Quart speaker has a longer depth than a Bose speaker so it presses again the power window support bar.
The rear deck -- I replaced the speakers in the rear deck with Kenwood 6x9s. I used an adapter from an Audi 200 with a Bose system to get them to fit right. It worked like a champ. For removing all the door panels and rear deck, check out the FAQ at audiworld.com. They have pictures and everything there. In the trunk I put a 12" Sony Mobile ES subwoofer in a sealed box. I don't like the boomy bass you get from band-pass boxes but I won't get into that discussion here. Check out other audio web sites for the difference between a sealed box and band-pass box. I bolted the box down with two metal straps that are bolted to the cargo net tie down bolts. I have the speaker facing away from the driver's cabin. It seemed to get the best bass response that way. I tried a few positions in the trunk before I settled on that.