Simplifying a jfet switching circuit? (Tube Works RT-922)

[stinkfeet]

Hi, I'm working on build a clone of the Tube Works real tube RT-922 that Marty Friedman used on rust in peace, but I'm not very familiar with Jfet switching. I was wondering if someone could help understand the switching circuit so I could get it down to the bare minimum and save some space and use less components. This preamp has three channels red for distortion, green for clean and a mode that stack the two. Thanks!