I think the site is www.levelten.com or some variation of that. They build some nasty gearsets for a variety of cars, for use at elevated power levels. They can also do custom-stall-speed torque converters for drag applications (I used to see them in the 300ZX world in my "past life" on cars built for the strip, and they were deadly effective when the stall speed was chosen with the car's powerband carefully considered).

If they make a gearset for the A8, it's going to be hideously expensive. That being said, if you're dead-set on spraying the A8, I'd spend the money to beef up the gearbox rather than end up with blown gears. Do as you will, but remember that these cars a) aren't intended for this use, b) aren't widely supported in the aftermarket to allow their use in this purpose, c) are known to have weak transmissions, and d) are scary-expensive to fix when they break.