I dinno about driving the vox, but as mentioned before the Marshall Bluesbreaker 2 is a gem of a pedal.
It's cheap, well built and sounds way better than any Tubescreamer I have ever heard.
It worked well infront of both my AVT 50 (semi valve preamp thingie), and my Fender Blues Jr. It also gave a friends Crate solid state amp a new lease of life.
Probably the most underrated OD pedal out there.