Subwoofer recommendations for mostly music


I don't know anything about subwoofers, so be kind to me! I currently have some sort of Velodyne hooked up to my system. It doesn't seem to add a thing to my system - possibly because it's crap, or possibly because I don't have it set up correctly! I would like to get another subwoofer anyway, so would like some recommendations. It will be part of my HT system, but I really want one that is good for music. I listen to classical, classical rock, jazz and World Music for the most part.

I will be pairing it with bi-wired B&W CM4 speakers (center is a B&W CMC) and I use a Rotel RSX1055 receiver. (I know a lot of people here don't like B&W speakers or Rotel components, but please don't suggest that I upgrade this stuff first - I can't afford to and don't want to!)

Budget wise, I would prefer <$500, if possible - used is fine.
oakiris
I really like what I have read about the Rocket Onix UFW-10. Great price and good looks, too! How important is it for a sub to be able to go below 25Hz?
Well, after all of this, and everyone's recommendations, I just bought the Onix UFW10. Your fault, newbie13. (j/k) I have spent the morning reading reviews by users, etc., and the Rocket really sounds like what I want. What finally tipped the balance, is that the company is based here in Colorado and I can pick up the sub from them tomorrow!

Thank you to all of you who took the time to help me with this decision.
I've a Velodyne DD-18 now after replacing a Velodyne DD-12. It does (as did the DD-12) wonders for anchoring my B&W CDM 9NT's... I listen to vinyl quite a bit and wouldn't think of turning the Velodyne off! I find it hard to understand how yours doesn't add some magic although you didn't put the model in your post. The Digital Drive series is OUSTANDING... and the 12" DD-12 offered me all I could want. The move to the 18" driver wasn't only done as I like what the 12" did so much I figure more of a good thing is a good thing!
Hi Sailfishben - At some point in this thread, I did post my Velodyne model - the CHT-8. nothing even close to the quality that the direct drive Velodyne's are reputed to have! Now you know why I wanted to replace it!

If I had the money, I would have gone for an ACI Titan, but my budget was pretty small, so, it's the Rocket for me instead!
can be used for sub duty. They are better than most of the plate amps that come with subs too. Like I said earlier the VMPS larger for 300 and you're done. You won't be wanting in bass quality or bass power. There's a reason they've sold thousands of those subs and they rarely are up for sale compared to how many are out there.