The Audiocontrol Epicenter supposedly reproduces the bass that gets missing from such as mp3 devices like the ipod when using the headphone out. I have used one before, and it does indeed make a difference, however it is a dangerous toy to play with. Every user I have seen use them completely use them wrong. You cant just turn all the knobs up, its very dangerous as it will damage your sub if you dont have a subsonic filter to prevent mishaps.
Im sorry that I dont know exactly what it does as far as the extremely technical aspects of it. But I do know it doesnt work the same way as an eq does.