The Audi 5000D/TD system is the one I described. The VW and Audi 4000D/TD is a 2 switch system. I have an Audi factory service booklet that explains the 4 cylinder/5 cylinder oil light differences.
Just for a clarification (sorry for opening up a dead thread) I believe you to be correct. There is only one oil pressure switch for the Audi, and the one Tom described on the oil pump is for oil temp.... lots of troubleshooting to figure all of this out.
I no longer get a low oil pressure light after replacing with a new sender, but now I have just started to get the light and buzzer when idling (goes away when I put any pressure on the gas pedal) so I'm hoping that it's from the sender as well and I don't have bigger problems.