Purchase this B5 Audi S4 from a local small dealership Dream City Sports Cars .
Removed stock stereo head unit and replace with a Alpine CDA-9885 with HD Radio, iPOD connection, and red light to maintain a stock feel.. all from CrutchField. If you want to get one of these units please use this Referral Code: pcer2-k1e4i-570c5)
Installed Apline Amp and two MTX Subwoofers within the trunk that I had on my previous MK3 Jetta VR6. Sounds awesome but lost nearly 1/3 of my trunk space... ouch!
Upgraded the rear fog light to light up for the passenger and driver side.
Upgraded both of my stock diverter valves to stock Audi TT 710N diverter valves, which I got from Achtuning. Seems like it has reduced some turbo lag. Took about 20 mins to install so it is for sure a good upgrade to complete.