I've never heard an Axiom sub. I have the base-level $500 SVS PB-10 and it's terrific. It's great for music and movies. It's detailed and not boomy but it can shake my house in films.
A very good friend has a $2200 Totem Thunder (SEALED) and I can't say I'm amazed by it. If I were you I would probably buy an SVS PB12-plus or SB12-plus. They are a little less expensive than the Axiom 500. The PB12-plus won Sound and Vision magazine editors choice award. The reviewers had some great things to say about this woofer, check it out:
http://www.svsound.com/Reviews/svs_pb12plus_sv_rev_1009.pdf
