That is after the fuel pressure regulator; however, I agree that it is most likely your fuel pump related, not regulator.

 

recently, I had a very similar problem where my 2000 a6 4.2 would die after 15-20 minutes and not start for about 30, but would crank and crank and never catch. It turned out to be the crankshaft position sensor was old and would overheat, shutoff, and have to cool. but this threw a code and i had fuel pressue, which leads me to agree that its probably the pump.

 

Similar problem on a another vehicle (not AUDI).. turned out to be a cooling temp sending unit... This car had 2, one for gauge, one for ECU. ECU one was bad and failed LOW making ECU think temp was > -20. Once engine warmed up it was too rich and died. No amount of cranking would start it again until the engine cooled off. Everyone including the dealer suggested MAF and Fuel Pump... it was neither.