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
a really good way to check out a sub... take the soundtrack to "mission impossible" with and without sub, a bad sub will obviously not blend seamlessly, whereas something like a Rel Stentor will make you sell firstborn to own.
At that price range: HSU VTF-2 (not the STF) the HSU VTF 2..hard to beat at $500
I just installed (and am still tuning) a REL Q108. It made my Von Schweikert VR-1s even more perfect. I set up a small listening room which is 13' wide the back to the speakers, 10' deep (my chair backs up to the wall), and 13' tall. The REL sits in the front left corner out of the way. I loved the VR-1s for their soundstage and clarity but with the lowest frquencies (below 35 Hz) reproduced by the REL, they are perfect. I don't really know its there, except that it seems the bookshelf monitors now how a fuller bass. Not bad for $750! I think the REL line is great for just music. Pick the one that pressurizes your particular room. Good luck!
I have narrowed the field down to the HSU VTF-3 MK2 or the ACI Force. I would love to buy a REL, but they seem to be difficult to find - only sold by Sumiko Audio in the USA and rather expensive - and would love to get the ACI Titan, but it is way too expensive, too.

Which would be better??
You will need an amp for it but for a couple of hundred you can get a used amp that would work for a sub. An Adcom 545 bridged would be perfect. You should check it out. The VMPS sub is very musical and plays down to 17hz. They aren't called the "Largers" for nothing. The HSU is also good but for the money that VMPS larger will do it all and then some.Final note, VMPS subs have had great reviews for 20 years and are known for having excellent bang for your hard earned money.