I cannot be a leader here. The Vac 300.1 was much better than my previous model VTL 750 Ref's. I used the VTL single ended, which may be against the majority as far as getting the best out of the VTL. It was not close though. The VTL was just not a good match with my speaker. Not to say that this would hold true with all speakers. I would imagine the VTL may be better with Wilson's , Avalon, or certainly Maggies. So yes, the answer IMO is system compatibility, and the preamp/amp synergy important also.
Good luck Tim.
Good luck Tim.