Willie-O,

I have a similar acoustic amp setup, except mine's a Laney, with a similar notch filter combination.

This may sound a bit crude and unscientific (coming from a scientist as well!) but what I tend to do is to stand with guitar plugged in immediately facing the amp (which is on a stand), crank up the gain and master volume until feedback starts to occur and then twiddle the frequency knob until this feedback is minimized. I then crank it up a bit further and further refine using the level.

Perhaps this will help. If anyone has a better why I'd like to know as well!

All the best,

moo