Folks,
Having had a factory fitted Sat Nav Plus for 10 months now (bought my A3 as stealer ex-demo car), I would have to say I would question all the hassle/pain you are going through to get this fitted.
Don't get me wrong, the Audi system is gr8, and I use it all the time, it is 95% accurate, but I would still seriously consider whether I would order it on a new car at £2,500. Yes its better than the VW version which is CD based rather than DVD, but £2.5k vs £500 for a hand held unit makes me think.
I would have to say, save yourself all the pain of a DIY fit on what is a lovely car as it is, there will always be something that will come up that will cause you untold hassle, and could end up costing you more than 1st budgeted, or do damage to the car, plus it still may not work as accurately as a factory fit. I have read lankyandy's post from ebay, and I would have reservations.
I would suggest you leave well alone an invest in one of these portable units you can buy now. My colleague has one, its brilliant, and in some aspects far better than the Audi Sat Plus.
Alternatively, hold fire until new year, I may well have my A3 forsale with factory fitted Sat Nav Plus!