Increase gain reduction on op amp filter
My goal is to modify this circuit so that the op amp filters are "full
  kill" (aka isolators) - meaning that when you turn the VR all the way
  down, it kills the frequency band completely.


Redesign using tunable notch filters as opposed to gyrator inductors and series capacitors. Gyrators are great for emulating inductance but it comes at a price of series resistance (R108, R112 and R116).

However, killing a signal completely is largely unfeasible - you might be able to get down to maybe 100 db reduction with careful circuit layout and decent components but you have to ask yourself if this is really what you want.