preamp mods bartolini dpdt

I've got a passive Warwick RockRass with two Nordstrand MM4.2 pickups that I've added a Bartolini NTBT HR-3.3AP/918 - Active/Passive preamp to, currently 3 Pots: (Volume) (Blend) (Treble/Bass Stack). Since I've recently destroyed my push/pull blend pot (for active/passive), I'm looking to build...