I've never listened to the Axiom subs, but from various reviews it seems that the EP series produce a very tight, clean, and crisp bass sound, which is much in line with the bass characteristics of the Axiom main speakers.

That said, I am pretty sure that the Hsu VTF-2 goes significantly deeper in the very bottom octave, with a higher maximum SPL available, than the EP175. However, I don't know whether the Hsu sounds noticeably "cleaner and crisper" than the EP175 driven within its limits.