I love my 2004 audi tt quattro. It is so quick! I have the rs4 wheels and micheline pilot sport 225/40/18. As of now I have an APR chip, APR catback exhaust, O.CT Front Mount Intercooler TTDA cold air intake, smoked side markers and Forge Diverter Valve.
I also have a custo matching yellow enclosure housing my JL audi w3 subwoofer and a rockford fosgate 400s. With the upgraded bose mid and tweeter system.
A picture of my system
And another of the enclosure
Here is a pic of my custom mounted bass boost controller 
