With a single turbo you can still get PLENTY of power. I think the main theory of getting a TT is get a more linear powerband, but the 2.5 is still a very tractable engine when turbo'd. Check this thread: http://www.i-club.com/ubb-files/Foru...ML/000209.html
There are actually a lot of single-turbo kits out; a search of these forums will give you more info than you want. If i could, i would probably go with Shiv's kit with TEC-II: http://www.vishnuperformance.com/index.htm
Best advice is to do the search, and ask other i-clubbers for advice. There are a lot of other very knowledgeable people that are glad to help; they've saved my arse plenty of time!