Don't think any off the audi's come with mechanical rear lsd's as standard.
(besides audi v8)
Although I'm not 100% sure about the newer models 2000->
Audi uses torsen center diff, mechanical device with wormgears,
no fluids like visco or haldex as volvo use.
You can get a torsen lsd from
Quaife (www.quaife.co.uk) for the read diff.
I think ZF also makes lsd's for this car.