You might also want to see this speaker just went up. I drove down to Tekton and got to hear it. It's a little larger than the DI, but definitely smaller than the Ulfberht. http://www.tektondesign.com/new.html
Tekton Polycell15
103db made with a different array which is more like a horn or waveguide. 15" dual woofers. He has it as a pro audio product. Seems ideal for flea-watt home use as well.
http://www.tektondesign.com/tekton-pro-audio.html