Have you toyed with transmission lines at all? They suprised me a while back as I had assumed (incorrectly) that a sealed enclosure would be the most accurate, and that ported would be less than ideal. I presumed a TL would be pretty much the same as ported. How wrong I was! The TL's I have heard have been by far the most accurate start/stop bass I've ever heard. They also seem to make smaller drivers sound even deeper on extension than larger drivers in any other type of enclosure. It almost seemed to good to be true - more accuracy with as much depth as anything else I've ever heard. I know these enclosures are much harder to design properly, but the pay off is quite something in the right room.