Scott,
The S4 b6 is a very beautiful car. I believe this is a 40 valve, 4.2L V8 that just sings a great tune through its' exhaust. With 0-60 times in 5 seconds and AWD handling it is an excellent performance sedan. Not to mention that AUDI has one of the best exterior paint jobs and offers the best interior quality features in the industry.
But 96,000 miles concerns me. You would probably know best how it was maintained as you already have a planned list of mods. The only complaint I hear about them is that they burn oil. I'm sure that some burn more than others, some probably burn very little.
Overall I think this car is a little mature for you. I mean I see a lot of old dudes like myself driving around in this kind of car, (lol).
I see you driving a new Mustang V6 Vert. Like the dark grey one on the recent tv commercials. You could always slap on a paxton supercharger for a nice exhaust note and have unbeleivable sleeper potential.