I had the bose too. I ended up replacing the front mids/tweets, and rear deck "woofers" with mids/tweets ... then I added a soundstream amp, installing it upside-down underneath the rear deck.

Really the absolute hardest part was the faceplate. If you can do that (or have it done!) then you're most of the way there. I just followed the FAQs on getting door panels and the rear deck off...

THE FAQ ON ORIGINAL STEREO REMOVAL DOESN'T WORK. If you have the huge angular factory stereo, just take it down to your Audi dealer and have them pull it loose from the dash a little ... they've got the perfect tools for it.

g

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Rio Car (40Gig) Blue/Red Face (Looking for Tuner!)
'01 Audi A4 2.8 Quattro