As far as what I could dig up, if you have a "sub" in the trunk, you have the DSP system. Also if you have three holes cut in the rear deck (looking from inside the trunk) this would also confirm the DSP system. To leave absolutely no doubt, you could pull out the display, and you would find the DSP module (small black box). Locating this would not be all for not, as removing it would return your DSP system back to normal (Fader, Ballance, etc.)
If your DSP controls don't work, someone may have already beat you to the aforementioned removal of the DSP box.