Looking for a very musical sub

I have a new array of DefTech ProMonitor 1000s as L/R and surrounds, with a ProCenter 2000. Also a pair of old Cambridge Soundworks Ambiance as rear surrounds, due to be replaced. A Pioneer VSX-1021 is the AVR

I'm very happy with the sound of this system in my small room -- 13x15, acoustically deadish with wall-to-wall carpeting and lots of upholstered furniture, with a 9 foot ceiling. The back of the room is completely open to the main living room, which is 13x25. The space is set up for two or three people, who are only 6 to 8 feet from the front speakers. The open back does remove back-wall reflection as reinforcement, however, so I tend to have to push the amps a little harder than you might expect in a space that small. OTOH, we're sitting close to the speakers.

The sub is my old Cambridge Soundworks BassCube 15, which is sort of the opposite of what I want: it shakes the house and everything in it, but it's not particularly tight or punchy. It's too big for the space, and it limits placement options.

I listen to a lot of music, including hi-rez music from BD, DACD, and DVD-A. Everything from jazz, classical, and folk to progressive rock.

The system is of course also used a lot for movies and TV, and I do like my action movies on BD, but I don't need those ultimate few Hz all the way at the bottom.

I'm looking for a sub that is:

-small enough that I can experiment with placement;
-very accurate for music -- this is the most important factor;
-appropriate for use with a crossover of 80Hz;
-fine for LFE, but earthshaking is not required;
-under $500. As far under as is reasonable.

All recommendations and discussion greatly appreciated!

What I have now is about 21" on a side, weighs 73 pounds. So, smaller than that. Let's say 35-50lb, and 15-17" on a side. And appearance is unimportant.

Thanks for the thoughts. Maybe I wasn't clear -- I value musicality above all else. I don't need (or even really want) sub-20Hz performance. Making my breastbone vibrate would just bring on another heart attack, and I've had all of those I care to!

I get that the adjacent spaces can't be ignored. At the same time, the listening position puts the front array in almost a nearfield relationship with the listeners (there are only two chairs). I am six feet from the front right and center channel speakers, and 9 feet from the sub.

The DefTechs are modest speakers, and the Pioneer is no powerhouse. If the sub can mate well with the speakers and give me musical clarity down to 25Hz -- which is more likely if it's small enough that I can experiment with placement -- I will be happy.

What about the Outlaw LFM-1? (I don't think I can accommodate two subs unless they were right next to each other in the spot where the current one is... and I'm hoping not to be locked into that one placement, which is below the right-hand window in a 3-window bay, located behind the TV which is sitting on an AV credenza. The credenza is flanked by the mains on stands, and the CC is in the credenza, tilted up, directly below the TV.)

OK, after reading through their website, Epik Legend goes on the short list. I wish it weighed less, but I understand why it doesn't.

Any concerns about the auto-power switch failures being reported in the Epik thread?

Anybody with a suggestion for anything smaller/lighter than the Legend?

There's more to accuracy than frequency response. The hardest thing for a large radiator to do is to stop vibrating once it starts. My current sub is very loud and goes very deep, but I question its accuracy. I've heard better, but I don't know how much of the difference is the sub and how much is the room interaction. That's one reason I'm looking for something with more placement options.