Although it's early days as your car hasnt been diagnosed, it it is the injectors, try and get the latest letter-suffix you can find (taking into account the price), as the early ones are crap by all accounts.
Certainly don't get earlier versions than you already have.
Here are two interesting threads if it turns out to be injectors....
http://www.pistonheads.com/Gassing/t...&t=991409&nmt=
http://www.audi-sport.net/vb/a6-s6-a...ce-please.html