From NonLinear Circuits website:
This module is based on the Intersound IVP Pre-amp. It is not a clone as the inputs and outputs are changed to suit Eurorack voltages, nevertheless the core sections are all there.
There are really 2 modules; one is the dual band shelving EQ (bass & treble), followed by the 4 band parametric EQ. Then there is the transformer based driver stage with an added VCA on the input to control the drive level and volume. The modules can be used separately or in series. The output of the EQ stage is wired to the switching pin of the DRIVE input jack.
Regarding the DRIVE section, the IVP Service manual describes it as a unique tube voicing circuit allows creative use of overdrive distortion. As mentioned, it is a transformer based circuit which has its own unique character and sound rather than sounding like a tube distortion.