What is the differnce between any dino and Audi Oil Quality Standards VW 502 00 and VW 505 01 oil?
To start with, VW and Audi have specified only synthetic motor oils for at least the last 10 years. And VAG issued a technical service bulletin to their dealer service departments back in 2000 or 2001, to use only synthetic oils in older engines where initially they allowed dino oils.
Whether you must use a particular VW-spec oil depends on a number of factors, especially whether your engine is still covered under a drivetrain warranty. If it is, then use an oil which meets that spec. After the warranty is over, do your research then decide whether a VW-spec oil or maybe an API-spec oil makes the most sense for your engine.
But whatever you do, don't cheap out by switching from synthetic to dino. Pick a good synthetic with the appropriate viscosity and features, and then see if you can't extend the oil change interval.
Lots of TDI owners have switched from VW-spec oils to API-rated 5w40 oils. The UOA results show that Mobil 5w40 and even Shell Rotella T 5w40 work as well and sometimes better than Castrol and Elf/Total. Not sure about Motul or Lubro-Moly, but I'd guess the M1 and other API 5w40s would be as good as Motul and LM.
I have a friend in Portland OR with an A6. I gave him a heads'-up on a great shop there, but I don't know what oil he's using.