Yes Duke, very intriguing design. Getting a transmission line right is not easy at all. Usually it becomes trial and error. The math only gets you near the ball park. The other problem as you mentioned is the bandwidth problem. With a 6 dB/oct crossover you would have to keep the crossover high to prevent overloading the tweeter. So either you are limiting the headroom of the speaker or you are asking the woofers to run higher then perhaps they should. If this is the case then a subwoofer system crossed on the higher side will help a lot. Otherwise, this speaker should image well and certainly has enough midrange power to go convincingly loud as long as the tweeter is kept out of the action. I'm surprised they did not use a 12 dB/oct crossover. Using an active digital crossover and biamping would be a natural for this design.
Relatively small speaker with a "big" performance: Role Audio Starship SE model
My review on the Role Audio Starship SE speaker just went up on the Stereo Times website. If you are looking for a floor-stander that's relative small, but delivers reference level bass extension, the disappearing act of a two monitor, beautiful timbres because of using all natural fiber based drivers, and quad transmission line technology, take a look at the review for the details on this excellent speaker.