Right then, a6 2.7t's were only ever available in quattro form, they either have a 6 speed manual or a 5 speed auto tiptronic!
The 98-01 models had 230hp regardless of gearbox and from 01 onwards when they facelifted them they had 250hp regardless of box!
With a very basic remap you will see about 320hp and anywhere from 320-386 lb. ft depending on the mapper!
The manual you wont have many problems with when it comes to power, when the clutch goes drop in a Rs4 clutch and your set!
However the autos can be a pain in the ****! I really wouldnt go mapping to anything above 320 lb. ft without upgrading the Torque converter first, or at the very least a decent tip chip, GIAC, Vast etc! Also Audi claim lifetime oil in the auto's, this is utter BS, change it every 60k at least to save on problems further down the line!
However dont let this put you off the Auto, ive got one and love it, you can manually re-code the box using VAg-com which massively improves the way it shifts, makes it a fantastic box IMO! If you wre on a quest for big power, its siply a case of changing the Valve body and the Torque converter to beefier items, then you can start thinking of K04's etc!
Be wary that turbo's will go, and when they do be prepared for a 4 figure bill if going through a garage, or if you do it yourself at least £600 for a set of turbo's, life expectancy of these units can vary from 100k to 180k miles, it all depends on how they've been looked after!
I love mine, its a ****** fantastic car, 322hp can see of most things nowadays, the repair bills can be big and sometimes frequent, afterall this is a sports saloon, but believe me BMW //M gear is twice as expensive, and when them big V8's go wrong, they really go wrong!