Without testing your specific setup, there's no real way to tell if the Vandy hookup will have a detrimental effect on your B&W's. However, based on my experiences as a long-time Vandy owner, and based on all the reviews I have read about the Vandy sub with non-Vandy main speakers, I'd guess that you will be pleased with the result. The hookup that Vandy uses between the main amp and the sub provides a way to balance the efficiency of the sub with the main speakers (I think the efficiency range is from 84 db to 92 db). Both of the Vandy subs (2W-Q and V2W) were reviewed in "Widescreen Review" magazine, and the reviewer stated the Vandy 2W-Q was the most musical and best integrated sub he has ever heard (he has 4 of them in his system). Both models earned nearly perfect 5-point ratings in all categories. There are to main differences between the V2W and the 2W-Q: 1) the V2W uses a 12" passive radiator in addition to the three 8" drivers; 2) the V2W accepts direct input from your pre/pro from either the line out jack or the LFE jack (which allows it be driven directly without the crossovers used in the 2W-Q). The V2W is about 3db more efficient than the 2W-Q, which may also be worth considering.
