Originally Posted by swamper8

Here is the best explaination I could find of what happens with reverse:

Ok here it is there are thoudands of these tiptronics zf trannies that this has happened to.In many cars not just audis there is a drum which houses the clutches for reverse gear, at leading edge of drum is a ring gear the wall was to thin and over time it splits drum cracks and cluth plates no longer will lock up. Tranny needs to be rebuilt and of course zf has a updated drum.

So there are updated parts to strengthen that part of the tranny. I believe there are also updated torque converters as well as that's the next weak link. Don't know how much HP/TQ a stock tranny can hold but I think it's a safe bet that they can't handle 450-500. So I would imagine you'll either have to pay for a purpose-built auto or find a manual car.