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.
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M80 v3, 2 x Emotiva UPA-1 Monoblocks, XPA-5, UMC-1 PrePro
Pro-Ject RPM Genie, Carver C2 Phono Preamp