Good musical sub under $500

I need to replace my crappy old AudioSource sub, my listening room is 12'X14' x9', hardwood floors (livingroom, not sure if furniture such as couches effect subs in absorbing sound as it does with mids & tweeters) . It will be 70% music so a accurate tight bass is a must,. It will be matched up with my NAD T752 A/V and Paradigm Studio 20v3s up front. MY present Audiosource I've had for years has to be turned to full volume just to add some low-end (Crossed over at 80, anything higher and you get vocals and such coming out of it, really crappy as I said lol). I had ordered a Velodyne DLS-3750R earlier in the week(cancelled my order) the more I read up on them it seems they are rather boomy and velodyne's good subs are the higher end stuff which are out of my price range. Used is ok as long as it's from a reputable dealer or owner (ebay is definitely out, really don't trust high end stuff from there). Suggestions?
I have recently heard the Martin Logan Grotto sub. It really seamlessly integrated with various speakers. There are a number of used Grottos in the market.
Just an update for anyone else interested in a UFW-10, the person I bought mine off had two (one I bought obviously) and the other he is selling now. He is moving up to the UFW-12, he's a great guy, a detective in NY state. The subs were only a year old and really weren't put into use until 6 months ago when he finished his HT setup.. It's a UFW-10 in Rosewood.

I got lucky and noticed he was thinking of doing this at another forum and e-mailed him asking if he was seriously interested in going that route and I would be very interested in buying one of his two.. he has pics, very nice, look to be 9/10 just because they are used.Just wanted to throw it our here for you guys, you've always been a great help to me and so informative!
A used Mirage BPS-150i is another consideration. The specs: 2 x 8 inch, bipolar, acoustic suspension, 150watts, 600watts peak. I have two of them and mate well with my Energy Veritas 2.2, ie. the high gloss black and of course the tight music.
I think that you will find Paradigm's own PDR10 or 12 to match very nicely with your Paradigm main speakers.
Sorry, no offence to anyone who owns them, but IMO Rockets = "mid-fi". (Their reference line is much better and more musical.) They will "do" for home theater but I sure wouldn't want 'em for serious music listening. The Rockets are not especially "musical" IMO.

Most of those rave reviews are from well meaning folks with little or no exposure to high end audio - people who are famililar with the kinda stuff you buy at CC or BB. They don't know enough to make meanigful comparisions and they mainly use Rockets in HT settings, so take the raves with a very several large grains of salt.

I suggest, if you will truly be using your system for 70% music, you stick with well-known "music" speaker manufacturers, preferably used e.g. REL. Otherwise you're not likely to get a "fast" and tuneful sub.

Another suggestion would be a used Alon Centris - very fast, tight and tuneful (and this one *is* musical). Probably $450 or less used.