Have a look at PSA XS15se (Jim Wilson again):
Now take a look at the JL Audio E112 (Jim Wilson). It is worse than the Ultra and doesn't come close to the much less expensive PSA!
I have a pair of these, and while the build quality is impressive and there is no doubting prodigious bass from such small boxes, I am very disappointed with these subwoofers' lack of musicality. I really expected such an overbuilt driver to provide exemplary performance, but not so. If you are all about HT and need WAF the JL Audio's are great!
Here are the Rythmik's atop the JLA's set up for A-B level matched comparison (2 Denon's with MultEQ XT32). I had the larger Rythmiks on the bottom, but wanted to be certain location was not the reason the Rythmiks were so much tighter - I reversed them and it wasn't.
Some may criticize that I am putting too much emphasis on the pulse response and ignoring output and extension, but, honestly, among the mentioned PSA and Rythmik subs and sb13ultra, I can't see reason to get too worried over output or extension - especially with music, but they would not short you on HT unless you were after the resonance SVS and JL Audio add (which can be thrilling).
In my frustrating experience looking for a truly good musical sub, this one chart made sense of everything I had experienced.
IMHO, anyone looking for a quality musical sub should be looking at sealed subwoofers from PSA or Rythmik.
I am assuming that other PSA sealed subs retain the pulse performance of the XS15se, and that the servo technology in the E15HP give consistent results with the other sealed Rythmiks.
If you check the Rythmik site you will note that their vented subs are listed as for HT, but not music. Brian seems to be refreshingly obsessed with music sound being just so.
Here is Jim's review and measurements of the LV12R:
http://www.hometheatershack.com/forums/speaker-subwoofer-reviews/67309-rythmik-lv12r-subwoofer-review.html
PS Do you still have the Focals? Do you run a sub with them?