axiom subs are good - hsu are better.

similar form factor, similar size - however, the hsu just has more features such as variable tunability (vtfs), generally larger amps, and are heavier - i like solid internal bracings!

however, if u want power beyond reason - the svs can do that! i have a 25-31PC+ and boy, it pounds like nothing i have ever heard... and for music, it can blend right in with my m22s.

JOEY's PC Sound System: Polk LSi7 (x4, mains and rears) and SVS 25-31PC+ (sub)