I was thinking three independent gain circuits that stack left to right (or right to left), and each gain stage 1, 2 or 3 could be used independently, in pairs or all three, going from low, medium, high gain or transparent to od to dist; Zendrive --> SD-1 --> DS-1.
Not good at making formats / diagrams, but something like this: though with all 4 control knobs on the Zendrive; one input, one output. Just 3 pedals in one box
View attachment 440238
Maybe on the last stage (stage 3), the smaller row of buttons could be small knobs for bass-mid-treble instead of a bright switch
thinking outloud.