the Vantage VG12R is a solid-state amp, is it not? If it is, I think you mixed up overdrive and distortion. Overdrive is the sound breakup when a tube amp is cranked. Do you mean that you're running the DS-2 in addition to the onboard distortion already on the amp?
Some good (and cheap) overdrive pedals are the Boss SD-1 and the Ibanez Tubescreamer TS7. If you have cash to spare, take a look at the more expensive boutique and well-known pedals, the Ibanez Tubescreamer TS9, TS808 and the Visual Sound Jekyll and Hyde come to mind.
:rock: