Any thoughts on the Fatboost vs3 tonestack?

[Rutger]

I would like to add a bass/treble tonestack in a ss preamp without loosing too much gain, and the bass/treble tonestack of version 3 of the Fatboost cought my eye. According to the description it could be a baxandall kinda tonestack. Normally you loose quite a lot of gain with that kind of tonestack, but the Fatboost doesn't seem to loose that much since it still has a gain of like 30 dB. Or would it be something similar like the active baxandall in the Boss FA-1?

Does anyone know how the Fatboost tonestack works (a schematic would be even better! )? And if you don't: do you have some suggestions for a proper bass/treble tonestack with minimum gainloss?