Totally understandable about the lack of time. The Rythmik that I sent a link to is actually a fully built sub with a custom 12" driver designed by a guy named Danny Richie.
If you are still looking to go to another company, SVS is DEFINITELY my first choice. I've heard an Elemental Designs sub that was fantastic for the price. The only thing was that it wasn't the greatest thing to look at. As far as Def Tech's offerings, I personally have never really been that impressed with their subwoofer offerings, honestly. They are overpriced and you don't get very good quality sound especially for what you pay.
Mark, I have very little doubt that the HiFi dealer backs the Def Tech as his personal choice and likely it is the best of the ones that he sells, but I am wondering if he's ever heard an SVS, Elemental Designs, Rythmik Audio, Epik, or even some of the Hsu Research subs. I've heard several Def Tech's including their flagship, Trinity, and it did not sound as musical (or accurate) as some of the subs from those companies I mentioned.