Hi RoccoLB
I would like to suggest that judging from your setup, it is likely the amp that killed your speaker. And the likely scenario is clipping, when your amp could not handle the high level input, the signal is clipped, with resultant output to the speaker that is much higher than the max amp output of about 100w. You only need one instance of clipping to blow the speaker. And without the proper electric gauges and meters, it will be difficult to test.
Years ago I blew a beautiful English speaker with my receiver with 100w because of clipping. And that was the nth speaker blown in my family, all for the same reason.
I could probably reproduce the outcome using other speakers by cranking up the output to beyond what the amplifier is capable of handling.
Similarly, our house came with a home theatre with a receiver not unlike what I had years ago, and the speakers are gone, most likely as a result of clipping as well.
Fast forward many years, I finally learn the importance of a good amplifier. I now have a pair of stereophile 600w monoblock power amp driving these tiny ls50 and they sound wonderful. The receiver for my theatre system is also replaced by a good power amplifier. No clipping, louder than my ears can take, if I wanted to torture myself.
I purchased 2 kef ls50 speakers and attached them to a Sony STR za2100es receiver. This sound system was for my 65 inch tv system. The sound was never that good. After a few months my speakers stopped working and the plastic fronts were blown out, completely broken. I posted the picture below. Has anyone else ever seen this. I brought the speakers and receiver to a local audio store and they are shocked that this happened they have tested the receiver with another set of speakers and found no problems.