I don't have a schematic of this either, but supposedly it's just two second order state variable filters.
Nice gut-shot by the way, hadn't seen it before. But the amount of opamps on there supports the theory. it's two channel, and each channel has a filter and something of a mixer. You need four opamp stages for each filter (which can be switched two LP, HP and BP very easily, in fact you can use the different outputs at the same time), some input stuff at the beginning, some mixing stuff on the end. And some railsplitting, because it is fed a single DC voltage. That should be it.
They are not know for fancy-nancy circuitry, just very high quality circuitry
The F2b is two channels of a fender input stage, the F1x is one of those channels with a crossover tacked onto it.
I can especially recommend the F2b, with a proper tube it sounds fantastic!