Please recommend a musical sub for me

Hello folks, I am wondering if you could recommend a sub for a music only system. I alternate between four vintage 80s speakers (Spendor SP1s, Spica TC50s, Linn Kans, EPI 100s) and all are classics and excellent within their specific parameters but they are all somewhat deficient in the bass. I alternate speakers depending upon my mood and musical selection. I am running Quad separates (909 power and QC pre) and listen to everything except classical. I would like a sub under $1000 (new or used) that is flexible enough to blend with these speakers for a music only application. I am not interested in reproducing earthquakes and sound effects, just a seamless integration and a fast, quick, precise bass that keeps pace with the music and doesn't seem to be disjointed from the speakers named above. My room is fairly small (13 X 14) so this might be an important factor in your recommendations. Thanks for your advice.
I love the TC50s - first speaker I ever bought, still have them. Kinergetics subs used to be recommended with them; they even had a crossover card specifically for the TC50s. Also, anything Audio Physic would be great (Luna, Terra). I remember hearing a small servo controlled Velodyne that cmae out in the late 90s that was very nice, but be caerful, as I have heard manyu vleodynes that were clearly not what you are looking for. Entecs will be fast, precise, and shake your floors if the music calls for it, but be sure to get a model that allows teh crossover to be set. Some early ones had a fixed crossover point set farily low, and would not blend as well with the smaller speakers you aer using.
definitive makes really quick, musical subs in your price range. hsu are great, very affordable subs as well. at the higher end of your budget, rel is a reliable, oft-praised choice.
Thanks for the direction, guys. Some of the ones on my short list thus far are:

Hsu VTF-2 or VTF-3

MJ Acoustics Pro 50 or Reference 100

REL Q108E or R205 or R305 or T1 or T2

Any comments from owners of these subs in a music application would be appreciated. I am confused by the REL ones in particular. The prices overlap in the Q, R, and T series and I don't know which would be best for music in a smallish room.
Given your room size, a REL B-3 should work well.
In your smallish room, a VTF3 is overkill. you might not be able to turn it down enough!
The VTF2mkIII I use is fine into even my 5000ft/cube room.
It even plays well with my panels.

Your problem may be a near-cubic room.
Approaches to 'fix' may include, putting sub close to seating position....this recommended by Dr. Hsu. I heard this in his cheesy demo room up in Orange County, Ca.
OR. a pair of subs to minimize standing wave interaction.
and finally:: Some kind of room modifications with bass traps.
In <2000ft/cube multiple subs may be nutty/expensive, so I'd go with 1st or 3rd rec.
Another small sub I came across in the forums is the Martin Logan Dynamo. Are there any users who can comment on its performance in a music only system?
I'm hardly an expert, but after a similar hunt I wound up with an SVS SB12-Plus:

SB stands for sealed box, which while not quite plumbing depths as low as ported boxes, many seem to prefer sealed for music. It goes plenty low...

Lots of connection options on the amp, a simple equalizer (that works!), and reasonably priced. I like what it's done for my two-channel rig.
I have a small music room with dimensions similar to yours, and have tried quite a few different subs to match with my 3A de Capo i's. Good room treatments are a MUST, and I ended up with 2 large tube traps in the front corners, 2 smaller ones in back, and 6 total 2'x 4' diffusion panels on the walls. The best results I obtained were with an MJ Acoustics Ref. 100MkII sub. It is very un-colored and non-boomy. It does not over power the room, and is relatively easy to adjust using the remote control and LED display. They are priced well below the smaller REL subs and have very attractive finishes.
Well, it aint small, but my Vandersteen 2Wq subwoofers are very musical - fast, clean, and easy to blend with my mains. Used, this sub can be had for under $1000, somtimes under $900.
The TBI subwoofers are by far the most musical I've heard. In fact they are the only subs I've heard that deserve such a qualifier IMO. Well, maybe the $10K Wilson Benesch Torus also.
You might want to search these threads for Velodyne SMS-1. It's a $450 subwoofer controller that I've commented on pretty extensively. Add one of these guys and the $500 sub of your choice (I use Rythmik, they're great but I suspect that there are many other fine subs out there as well) for excellent results.

Good Luck

ACI Force XL. I find it to be articulate, clean, and very musical. I have paired it with Spendors and got excellent results.