If you want to get a rough idea of what can be done with the 3.2 V6 engine, check out www.r32oc.com. Obviously the ready made packages talked about on there are for the R32, but in principle, if your pockets are deep enough, then twin turbos can see 600BHP! ;o)
This has been discussed a few times in the path. The 3.2L VR6 motor that's in the R32, A3, TT 3.2 is more able to handle boost than the 3.2FSI that's in the A5. Lower static compression, cast iron block, etc.