Subwoofer sensitivity, fastness and fine separation

Devon Turnbull of Ojas Audio was recently interviewed by Steve Guttenberg and Ken Micallef on his enormous subwoofer utilizing a high sensitivity 31.5" Fostex “superwoofer” and made some interesting points relating to the fine separation, “musicality” differences in subwoofers… How a high-excursion subwoofer in a relatively small box does the job well in extension but easily makes the difference between a double-bass and a synthesizer hazy, etc.
It’s true, a subwoofer shouldn’t be just a bass machine, it should have optimal nuance separation integrating with the stereo speakers’ nimbleness and I guess this really translates to having the quickest, lighest easily responding drivers and this equation doesn’t obviously fit well with high excursion, well, depending on the mass of course.
Wilson Benesch makes the Torus “infrasound generator” (that doesn’t actually go all that infrasonic), with toroidal 18" carbon fiber woofers and its purpose is basically to be as nimble and well-integrating as possible with any speakers, horns, what have you, down to the lowest registers. It IS extremely costly, it is well cheaper to build a huge subwoofer with the Fostex superwoofers. But it is “compact” and certainly interesting technology.

Share your experiences with different types of subwoofers and their ability to keep up with and translate nuance, and philosophies involved.
I’m thinking of building a subwoofer and would really like to have it be quick and well-integrating, if you know to recommend drivers especially suitable, please do.