Well, even after reading the other thread, I'm not clear on whether these speakers are powered by an external amplifier, or if they are self-powered. You talked about running only power wires to the ceiling.

If the speakers are self-powered, than any equalizer made for home stereos will do just fine. It will have line-level inputs and outputs. You can get them at any home stereo shop.

If the speakers are powered by an external amplifier, just turn up the bass and treble on the external amplifier. If it doesn't have a bass and treble control, buy one that does.