Obviously, the A6 was pretty heavily modified, then.
There are a lot of options you have. Going off only what you describe the events to be, I would say sell your car and pick a different platform, or write a check for $15K+ to play with the big boys.
To give you a decent bump in power yet still maintain decent reliability, consider going E85 (if available) or adding alcohol/methanol to the car.
Making full use of the dyno time (and prepping yourself for a bigger turbo, if you choose, down the road):
Fuel pump (one that's ethanol-compatible)
ID1000 Injectors or Aquamist HFS-4 meth kit
A good ELH (link)
A good TMIC (e.g., ProcessWest or Spearco)
EWG uppipe (e.g., Grimmspeed)
Boost control (EBCS + MBC)
If you go E85, you'll need larger injectors. If you go the methanol route, you shouldn't need injectors (unless you upgrade turbos down the line). If that doesn't give you enough of a bump, your only other option is to do a turbo swap (which will require injectors and at least a built shortblock).