There are flaw's in your story about the new engines which will be added to the B8's line-up.
The 2.0TFSI engine will have 200 and 250 bhp and will be availeble with FWD and Quattro.

3.7 litre is not possible with the present FSI/TDI V6 engine line, they have a volume limit of 3.2 liter, otherwise Audi had increased the V6 engine volume of the 3.2 FSI and put it into the Q7 instead of the Volkswagen 3.6 VR6 FSI engine..

The V6 Bi-turbo FSI engine will have 3.0 litre volume and can be seen as the successor to the 2.7 litre V6 Bi-turbo S4/RS4 engine and will have between 320 and 350 bhp.

The S4 will keep the same 4.2 litre V8 FSI engine but will get most likely "Valve-lift" added to it with a 3-5% power hike.

For the new RS4/RS5/R8 engine Audi have 3 options:

1) The same 420 hp 4.2 litre V8 FSI engine. (RS4/5)
2) This same 4.2 litre V8 FSI engine with Valve-lift and ± 440 hp. (RS4/5 and R8 upgrade)
3) A 4.2 liter V8 TFSI with ± 470 hp. (RS4/5 and R8)

Hans.