Notice the low value on the Blend knob. Also the relationship between the Treble and Presence knobs. Level is set at unity gain. Drive is set to give some noticeable, warm OD. But I think the low blend knob prevents farty, blown speaker type sounds on low notes while still giving at buzzy, tubey warmth to notes in higher registers. It even sounds good with some slap. I think I may have cracked it.