If you want to maximise bass then horn-loading is the way to do it.
But we're probably only looking at 3-6dB over a ported box.
Taking crisis' inputs the other way around, it may be easier to double the power of the amp and speakers than optimising a horn.
If you can think in 3D, then horns are actually quite easy.
I was 15 when I was introduced to a special horn-loaded Tannoy enclosure made out of concrete. It was amazing how much extra bass for the same input power.
A modern interpretation to hear what can be done are the little Bose radi/cd units. These have 3" drivers and a horn winding it's way around the case and it is astounding the amount of bass produced.
But, I accept that you're maths needs to be spot on to play with horn designs I just hoped that the java applet the guy had written might have made it easier.
Sorry it didn't
Why not take crisis' inputs and come up with what you think would work for you and we can gently critique it here for you.
Cheers
Peter