The emf from one speaker is certainly not the same as 36 speakers when you present that load with another load, IE:the amps outputs. Every amplifier must overcome the back emf given off the subwoofers motor(fixed magnet/coils moving makes AC volt's and amps) Normally the back emf is so little it is a non issue so that is why you never hear about it.

But when you present that wall of woofers with resonance(sound waves that they will have the most simpathetic vibrations from) that 36 motors can turn out some voltage and some nice current. Now who knows if that current was enough to overdrive the amps current output but I have seen it before. Without actually seeing what failed on the amp we can only guess as to what caused the failure.

Do this as a small test, place a sealed enclosure with a Q of .7 in your cabin with a 15 or 12 and play the note that resonates your subwoofers the most(visually) then take a multimeter and measure the output at the 36 subs speaker wire that the amp was connected to. You will see X amount of volts, you then place a resistor across those 2 wires that has the approx impedence rise of your amp/sub box then measure current output. Try it its kinda fun