LeeJ,
How are you plugging the mic in to your VS. I don't think that thing has onboard pre-amps (my old VS-840 didn't) so you may want to look into a decent mic-pre amp, even if the unit has XLR ins they might not be giving the boost you need.
And if you are going to record vocals you should really look into a Large Dia Condenser. Their are some fairly good units out there at some really reasonable prices, some even take batteries so you don't have to worry about phantom power for the mics.
-k