I would go with APR, AWE, Revo or a name brand Audi tuner. Superchips has a somewhat questionable track record. You're problem is going to be the TDI. Most of the bigger tuners focus on the gassers. I googled "A4 2.0 TDI chip" and got tons of hits. Just do your research and get an EGT guage or you might melt your manifold. Good luck.
Search Audi A4 Questions
Audi A4 Experts