without a doubt, definitely, go get a SUB!!! and yes, the HSU is a very nice sub, but maybe overkill for 2 channel audio only. that being said, you certainly could keep it for when you go 5.1 or 7.1 or whatever you end up with. when i turned my sub off...the impact was just not there compared to with it on. i mean, the M60Ti's sound great, and do a decent job of bass, however, they just can not compete with a stand alone sub for bass management...depth, or quality

Axiom M60Ti Infinity 2000.6 x 4 Infinity RS1 rear Infinity CC200 HSU VTF3 - MKII