You could sell privately and get the buyer to pay the finance company directly to clear the finance and pay you any extra over the settlement figure or you pay any extra to cover negative equity.
You could get a settlement figure and see how much Audi will buy it off you for (they will pay finance company and you'll have to add own cash to cover any negative equity if there is any)
I assume we buy any car and similar businesses would do the same as the dealer.
For reference when we bought the wife's tt we were 18 months into a pcp on a mini jcw. We called our mini dealer and they wanted to buy the car back, cost me £1500 in negative equity but then we ticked almost every option buying the car so wasn't too bad. Was very simple, paid them the negative equity sum and they cleared the finance.