It uses a special algorithm to increase the lower frequencies without distorting the upper ones. It is better than just Bass control or the fader because it "does the right thing" if you are trying to get more kick out of your subs.

It's probably a lot simpler than you're making it out to be.

It's merely a bass boost that lessens as you turn up the volume. Its purpose is to compensate for the fact that low frequencies seem to get lost most easily when the stereo is played quietly.

One of my dreams is to one day be able to adjust its parameters on the empeg. Right now, it's not "doing the right thing" in my setup. Its boost frequency is too low for my system (makes the sub work too hard in the super-low frequencies without really properly compensating for the loss of perceived bass in the 100-300hz range), and its ramp cutoff positions aren't where I'd want them to be (too much bass boost when volume is cranked very loud). So I end up not really using it on my system. But I understand that it works great for others, so there you go.