I had not considered the possibility of supersonic oscillation. That takes a highly reactive load, and I have not heard or encountered that outside of electrostatic loudspeakers.
When your 12" Altec burnt out that must have been an oscillation in the audible range, as the crossover would have blocked a suprasonic oscillation. Much more likely the burn out of a 12" driver was due to a huge episode of DC offset. If the top end of the speaker system was intact, I can tell it was DC offset for sure, as the series caps protect all the other drivers, but not the woofer. That I have seen at least twice.
However if Emotiva have designed a speaker that is not electrostatic, that presents such an a reactive load that it sends an amp into oscillation, then they still need some sort of Darwin speaker design award. It would be obvious, in both the modelling and measurements of impedance and phase angle. I really find it hard to believe that is the problem. In addition he has driven it with an Emotiva amp and a receiver. When this event occurs it usually takes out the amp as well as the speakers. I would not have thought a receiver would survive this insult. I doubt oscillation is the answer to this.