I am looking at a 2001 A5 B5 with the 2.7T and auto trans.
My plan for the car would be to upgrade the turbos similar to RS4.
The auto trans will at some point become the weak point.
How much turbo (Engine HP, Torque) can it handle?

 

K04s are about the limit of that trans. You might even want to do an upgrade to stay on the safe side

 

Hm. Does K04s mean RS6 power levels, because it looks like its the same 5 speed tiptronic used in the RS 6 (4.2 V8 twing turbo, output of the V8 engine: 331 kilowatts (450 PS; 444 bhp) at 5,700 to 6,400 rpm,560 newton metres 413 ft·lbf of torque).

I won't exceed the power/torque with my upgrade plans!

5HP24A

Four-wheel drive version used in Audi (quattro) and Volkswagen Passenger Cars (4motion) marques of the Volkswagen Group:

• 1997–2003 Audi A8 (D2) 4.2 V8
• 1998–2003 Audi S8 (D2) 4.2 V8
• 1999–2003 Audi A6 (C5) 4.2 V8
• 1999–2003 Audi S6 (C5) 4.2 V8
• 2000–2002 Audi S4 (B5) 2.7 'biturbo' V6
• 2000–2003 Audi A8L (D2) 4.2 V8
• 2002–2004 Audi RS6 (C5) 4.2 biturbo V8
• 2002–present Volkswagen Phaeton (Typ 3D)