I just hook up my new Onkyo 602 with my old speakers(tower JBL in front and book shelfs design acoustics for center and rears). The new receiver really pushes my towers. I hear bass that my old pioneer receiver could not produce. I played a few movies (star wars, T2, etc.)and it sounds real good.I also played music as well and it sounded good. My question is: 1)Do I need a sub? 2)How much of a difference will it make If I get a sub? Right now my setup is 2 fronts 2 rears and 1 center so its not 5.1 but still sounds pretty good. PS I might change the fronts to book shelfs next year so I'm sure I will need a sub then but what about now?