Power Scaling

[FL6]

Aside from just turning knobs, how do you approach using an amp modded with London Power's power scaling?
I obtained an amp from a friend and it's a custom amp, it has 2 dirty channels with 3 gain stages.
Each channel has a preamp gain knob, a channel volume, a master volume and a Scale knob.

I understand it's to help get power tube saturation at low levels, but just curious how these 4 knobs interact with each other?