Man, this is versatile.
Long story short, I built a 2nd BSIAB II (my main one is being rebuilt as well), with a couple of mods.
1) My tried-and-true removal of the two .0022uF caps in the low pass filter at the end of the circuit
2) I replaced the values in the stock BSIAB II tonestack with that of the AMZ Presence Mod #1; I labeled it 'Contour'
So, it's a four-knob BSIAB II. Where it really shines is that it goes from chunky, low mids, to a full-mid crunch, to an almost DS-1-like scoop. SO many sounds that I wish this thing had MIDI presets. The tone and contour are VERY interactive. Mainly, I would get the contour where I wanted it, then adjust the treble with the tone control. The 'Contour' does drop the volume a little when you rotate it fully clockwise.
I love the sound and versatility of the BSIAB II, but this really expands on that. I highly recommend it. I didn't want to go TOO over-the-top with this post, so feel free to ask any questions.