Here's the scenario:

My drum fill consists of 2 X 18" JBL subs, and a bi-amped, monitor wedge with a 12" JBL low driver and a 2" JBL horn. My subs are powered by a Crest 8001 in bridged mode. I checked the headliner for the show the other night, and my subs were rockin. When the main support had their sound check, their drum tech asked if he could use my drum sub amp to power his butt thumper. ( I should mention here that I have done this before with no problem. ) I plugged him in from his In Ears console straight to my amp, and went about my business wiring the stage. Two minutes later, my FOH guy told me that I smoked my amp. The amps are kind of old and tired, so I assumed first that it was just time for it to go, and brought out a spare. I hooked him up again (keeping my amps at half unity this time) and as soon as the drum tech hit the kick, it blew THAT amp! AT HALF UNITY! Two amps smoked. Luckily, I try to follow the old saying "better safe than sorry" and had 2 spares stuck away. So the show can keep rockin.

My question is this:

Due to a crappy power situation in my building, I have to run my drum sub signal with a ground-lifted XLR cable. (to eliminate a ground loop that causes a pretty righteous buzz). Could that have caused my amp to blow? Could a lifted XLR create some sort of problem so that the input to the amp is what created the light show on my amp? Or was that dudes thumper the issue? I suspect it was the thumper, but I just want to be sure. .can anybody help me on this?