I'd say it's probably gonna be a bit of a headache to fit.
From the research I've done around my Audi A4's system, it seems like some Audi's were offered with it as either a full or part system. And it uses a power amp for each speaker, so you have to get pre-outs connected from your head unit. This meant if you wanted to use a non-OEM head unit in the car you need an expensive ISO loom to connect to the BOSE system.
If you're putting a TT or A3 dash into a Mk2, then completing it with the original Audi/Bose head unit and speaker system would be neat, but otherwise, I don't think it'd be worth it as you can get just as good results from other manufacturers.