Bass is rolled off at the recording process. What the epicenter does is digitally restore missing information. While ideally yes, it prefers a full range signal, it has and will do wonders even if given a low pass signal. Correctly pointed out above as to how it works is simple. It looks for octaves to extrapolate the signal. It already has the signal to work from remember, it is there, it just may be missing amplitude at the lower frequencies or it may indeed have been rolled of at 6, 12, 18 db octave at the recording process. Now this is not a brick wall filter that shuts off low bass, it means that the frequencies are there, they are just not pronounced.
What it does it takes the lower frequencies and for lack of better words, digitally remaps the lower frequency spectrum. If you are looking for a 40hz note, it starts about 4 - 5 octaves up and digitally extrapolates what the wavefrom should look like. So it goes looking at the range of frequencies at 40hz, 80hz, 160hz, 320hz, 680hz and finally 1360hz should it go up 5 octaves. This is when having the full range signal to work with is beneficial to work with as there is much more to derive a more accurate waveform from as compared to 120 hz and down. Once it has reconstructed the wave form digitally, it reinserts it into the signal and onwards to the amp it goes.
Now the epicenter has a control for it. It is best used in moderation, as volume levels go up and you move closer to the mechanical limits of the sub, using a epicenter may take you past the mechanical (and thermal) limits of the sub. Hence the old name for it, sub destroyer. If you are abusing the old control knob of the epicenter, you are going to go through subs. Use it in moderation and enjoy what it can do for your system.
Remember the chicks ***** on Airplane? That is what an epicenter used properly can do to a system, it can take you from having bass to getting shaken like a bowl of jello in a earthquake.