The R8 V10 is a NA engine so is not particularly high torque. However it also uses a different gearbox (the OBZ) so you can't really use it as a comparison. Nevertheless I suspect that not only was torque rating only one of many reasons for changing to the ZF, but the concern was open to misinterpretation. I assume that the B9 range still uses the DL501 box, and it its latest version it can handle 600Nm which is more than enough for the S4/S5 single turbo V6. However you don't have to look hard to see that that Audi have had many problems with this gearbox and so the decision to reserve it for models with engines which will put it under less stress than the S-models would seem a sensible one. The advantage of the ZF is that having a viscous coupling (torque converter) it can absorb the shock of gear changes at high torque in the same way that a big rubber band would. So not only will the risk of reliability problems be reduced, but if there turn out to be any then Audi can pass them onto ZF.
I have not driven a car with a ZF8 gearbox either. However considering the investment made by that company, their specialism and the fact that it is used in a huge variety of different makes and models of car, I cannot believe that it is not a damn good box. I am guessing, but I suspect that if/when I test drive the new S4/S5 I shall struggle to notice the difference in speed of gear changes. But I can't believe that I will not feel the elasticity of the oil transmission, but on the positive side I am intrigued to find out what the impact of the torque multiplication is like. But the bottom line is that this is the box it will have and if customers really don't like it they won't buy one. Just like IF Audi don't do a manual version for the US market the folks there will have to decide if that's enough to turn them away from the B9 S.
I find the comparison of dual clutch vs torque converter interesting, so perhaps I can finish by reminding people that ZF make both.
This is what they state about their torque converter box: "With the development of the new 8-speed automatic transmission by ZF, the focus is not on the number of speeds but rather on the minimization of fuel consumption. The new 8HP 8-speed automatic transmission, which was designed to be more lightweight, sets new standards for flexibility, efficiency, and economy. It is an excellent example of how the power of innovation can create a new classic design."
Whereas this is what they state about their dual clutch box: "The 7-speed dual clutch transmission makes especially sporty driving performance possible: direct drive and lightning-fast gear changes without interrupting the shear force. The car "sits right on the gas". It also achieves fuel economy better than that of a manual transmission thanks to its excellent fuel efficiency."
