I've also been in the market for a sub. In addition to the Axiom EP 175, there are several other subs I've found to be very musical: Def Tech ProSub200, Paradigm PW2200, ACI Titan II, Velodyne HGS II 10 and 12. A friend owns the Titan; I feel it is the most musical of this group, but the cabinet, while by far the best looking, is a bit large for our room or I'd probably be out of the market. I listened to a number of others I was less impressed with musically but may be great for home theater.
To pass on a suggestion someone gave to me, regardless of how little or how much you're going to spend on a sub, spend time in a good local audio shop listening to very expensive subs - $3000, $4000, $5000, etc. Listen to CD's you're very familar with and featuring a lot of bass - not just rock bass guitar but also organ music, classical bass fiddle, bass drum or kettle drums). See if you can get the dealer to turn off all speakers but the sub. Get to know what a good sub sounds like. When I went back to listen to subs in the mere-mortal price range, I felt I was a bit better at listening and better able to decide what I like about a sub and what I didn't. Hope it helps in your comparisons.
