I'm sure its not impossible, just depends how different the floor pan is on the 8v ( its a different chassis) and how much fabrication and cash you want to throw at it.
The sports exhaust on the 8V is approx. £1500 from the secondary cats back when bought from Audi as parts.
A couple of things you would need to consider...
The batteries are in the boot so you would have to check they haven't tweaked the layout for the 8V dual oval outlets.
The active exhaust flaps are electrically motorised on the 8v not vacuum operated, so you would need to sort that.
Unless you chop up valance, you will need to do something with the RH tails.
I guess you could keep them and just get them turned downwards to remain hidden behind the bumper.
Then there is the existing tails, if you turn one set down to save cutting the valance, you would need to swap out the 8V oval for the 8P twin outlets.
I think cutting the valance and putting the twin ovals would look horrible.
However, done properly, keeping the original RS3 8P oem tails, and getting the 8V back box in there with suitable vacuum operated flaps, would be interesting to see,