Quality small sub for HT and music

I am looking for a new sub for my theater system (which doubles for music.) I currently have: Parasound C2, Aragon 8008ST, Acurus A200x5 and A200, Cary DVD-6, Boston Acoustics Lynnfield 500L (for mains) and 300L for centers, Boston VRMX (sides), Definitive inwalls (rears) and a Boston PV1000 sub.

The Boston sub does well, but I want to improve; but don't want to break the bank! I just added a M&K MX-70B for a rear sub (which improved the coverage in the room substantially.) Now I want the next level. No big, boomy bass though.....high quality and tight are paramount. Size is also very important....must be relatively small.

On the short list is the ACI Titan II, Infinity Interlude 1.2S and M&K MX-700. Want to spend $1300 or less.

Anyone with some words of wisdom? Should I just keep the PV1000?

I just checked out the new Velodyne digital subs. Very nice. Small. Attractive. When it comes time for me to get a new sub, I am going to be checking these out real close.
I've heard about the Velodyne DD subs. Good...but very expensive. I'm leaning toward an ACI product. However, rather than getting a Titan and matching it with the M&K MX-70 I just added, I'm thinking about returning the M&K and getting a pair of the ACI Force subs. I like the coverage that 2 subs provide in my room and their small size will integrate well. Also...probably easier to blend 2 of the same rather than the Titan and the M&K.
Seems like I'm answering my own questions here, but for those interested.....

I ordered a single Force today. Going to test drive one before springing for a second. The Pres and founder of ACI (Mike Dzurko) swears that you can't tell the difference between a Force and a Titan, other than sheer output level (the Titan produces 3db more.) If this is the case, I think this may be the perfect unit...for me. It won't arrive for more than a week and then its got 60 hours of break-in. I'll post some thoughts once I've had time to evaluate it.
John, I own a Titan and I was able to borrow a friend's force for several months. They do sound identical, and that's a good thing, because they both sound terrific!
I am in a similar predicament. It seems like in addition to the Velodyne digital series subs, ACI and REL are the companies to check out.

You must listen to a Hsu VTF-3. Simply the best bang for your buck subwoofer made today. I have the VTF-2, but if your budget is $1300+, then the VTF-3 is the one for you. Seriously...don't think because it's only $850 it's no good. I listened to a ton of subs before purchasing my Hsu...I ended up paying FAR less, and getting a tighter, faster, clearer sub.

Email Dr. Hsu with any questions. He'll get back to you quickly. They mostly sell online, but they've started to sell through dealers. http://www.hsuresearch.com
Are you AT ALL interested in selling the 300's???