Actually as I understand it, the Blackstar uses a 12BH7 and an ECC83, which if memory serves is the British name for a 12AX7. It is all analog but not necessarily all tube as Tung pointed out. My uneducated guess is that it uses the 12AX7 and then adds in opamps for more grit. Basically it's a built-in distortion pedal. The preamp is essentially one of their HT-5 pedals. Otherwise if you wanted to get high gain from tubes, you'd have to add a bunch of preamp stages like a Soldano which would make the amp much more expensive.

From the marketing-speak that I've read, the ISF seems to be a very fancy contour control. But instead of just moving the mids it moves the whole tone stack. Theoretically if you turn it counter clockwise it sounds more American (Fender?) and clockwise it sounds more British (Marshall?).

All's I know is that I want one.