It's a twin with a VX EQ, I got it at gtrgear and here is what they tell about it :
"more Dumble-like, less punch as Twin - chimmery thick clean/breakup Voxy tone"
I don't know about the dumble as I never heard one, but I'd say that the second part is right.
I got a Bman now because I like a warmer/darker sound.
That is a question I will leave to Jeff or Bruce to answer. I have read that most of the classic preamp designs are similar. The classic Fender and Marshall circuits are both derived from the same design.
Maybe one of the experts will chime in .......(thats you Jeff )......