Subwoofer upgrade?

I don't know your subwoofer specifically, but many people try adding insulation or some kind of foam material inside the box to adjust the sound response. You could try searching other threads here or on Audio Asylum.

Or just buy a REL.

Golfnut, what is the alignment of the subwoofer?

By that I mean, sealed, ported, etc. And, if ported, are you able to be more specific; 4th order, 6th order...

Also, can you give me the dimensions of the box, and any driver specifics?

If you are willing to do some "tweaking", you can get to where you are looking to go.

Aside from where I am going with this, if your subwoofer does not have spiked feet, these will tighten the bass response up a bit.

Which Mirage subwoofer is it? I have a pair of Mirage's BPSS-210 subs with their FX-3 crossover, and they are not "boomy" at all. Very tightly controlled and "fast".