It may have been a power spike/surge of some kind; this can be ruled out easily: was the amp unplugged?
The reason I'm thinking about this possibility is that I went through something like that, but with much dire consequences. My two Emo monoblocks are toast (displaying different behaviour), as well as the 2 M80: one has the woofers gone, the other the mids and the highs. I somehow doubt that in my case the actual drivers are one; I'm inclined to believe that the crossovers are at fault. We'll see, as both speakers are back to Axiom. The casue for my case was a lightning storm; if a high enough current is present, it will arc over whatever protection you may have. My amps were both plugged into a dedicated 20amp line and into a Monster power surge protector; also, I understand the Emotiva amps have surge protectors in them.
What happened in your case is that you had a destructive surge come in from the outside line and was seeking to find earth, in this case it was your amplifier. Internal protection found in the appliances and those found in surge and UPS strips are NOT rated to handle destructive surges and are easily overwhelmed as you noticed in your case. Plug in surge protection strips and the protection found in UPS strips are useless.
Despite the fact you still feel vulnerable, the good news is this problem could be solved in the future by purchasing and having an electrician install a "whole house surge protector" to your inside panel and grounding it to your homes single point earth ground. These protectors meet proper electrical specs and code and are rated to handle high energy transient voltage surges.
A whole house surge protector wouldn't have let the surge inside your home to begin with. A proper protector such as these would have just harmlessly grounded the surge outside. You would have never known the surge even existed.