Cleank,
The wedge-shaped asymmetrical enclosure effectively controls internal and cabinet-wall resonances (it prevents internal standing waves from forming), but there is additional bracing as well.
Besides, that cabinet-knock test tells you about as much about a loudspeaker as kicking the tires on a car!
Over the years, I've heard numerous lousy speakers that were extremely well contructed and braced, including a famous American high-end brand that had a sloping front baffle made of stone. If memory serves, each speaker weighed 300 lbs, and the treble resonances were enought to fry your ears!
If you have reasonable control of cabinet-wall resonances (and the M80ti's have that), what matters is the careful adjustment of drivers and crossover (as well as driver design and selection) to get smooth, linear frequency response over broad lateral angles (vertical dispersion is important too, but not as important as lateral).
The aforementioned is vastly more important than cabinet-wall resonances, which pale into insignificance by comparison to achieving ultra-smooth response through the midrange free of glitches, spikes and suck-outs. . .
Regards,
