I tried not to respond to this thread, but I've seen too many threads like this recently...basically it's the following story:
person buys a dream car (fill in the blank, but usually costing less than $5K), then a few months into ownership realizes it has some issues and complains about XYZ, then throws out a statement that they don't care for the car and will get another Audi (usually 20X more expensive than the original car - RS7, R8, etc...).
Sorry but i'm doubting that you plunked down whatever you did on a 15+ year old C5, when you could actually purchase an RS7...the 2 cars are worlds apart!
BTW, here's the other thread, that the OP here reminded me of: http://forums.audiworld.com/showthread.php?t=2860432
Lastly, with the issues you've described, I doubt the trade in for the RS7 will get you car cover for the new ride.