I have a pair of Vandersteen 3A Signatures. My listening room is small (25 X 13) and I listen at moderate levels. I have heard good things about the Vandersteen/McCormack pairing, but I'm also a big fan of NAD. I have the opportunity to buy a used S200 or a used DNA-125. A DNA 225 is too expensive. The pre-amp and cables will also be upgraded, but I don't know to what. Source is NAD 720.
In your position I'd definitely go for the McCormack DNA-125. If you can find a McCormack DNA-0.5 with the Rev. A mod. from Steve McCormack that would be a great amp to build around or even just a stock DNA 1.0.