Just to clarify, what do you mean by bass? What main speakers do you have and what crossover frequency is set?
What we hear as 'bass' is usually a combination of the very lowest frequencies (below, say, 30 Hz) which are typically reproduced only by a subwoofer, and the somewhat higher frequencies (150 Hz or more) which depending on the speakers and settings might be reproduced by a combination of all the speakers. For example, I have a (non-Axiom and not very good) subwoofer with LFRs and a VP180. I set my fronts as "Large" so most of the bass I hear probably comes from all the mains plus my sub - in fact my sub may even roll off more steeply than my fronts!