I've been considering this question as well - dreaming up a small rig with F-2B & SF-2 - I personally would go through the F-2B first for the sound quality of the unit, EQ it the way I want, then for myself was thinking of using the SF-2 as a fancy crossover - low-pass on the neck pickup (low frequencies if going mono), hi-pass on the bridge pickup.
It might sound cool to put the SF-2 first and kind of overdrive the F-2B but that might not be the sound you're going for.