Paul, you may be the perfect person to ask this question.
I have an M&K MX-100 subwoofer in storage at the moment (because it is broken). I have had it fixed twice. I had it for several months (after I initially bought it) before I had a single problem with it. It sounded great, had awesome low frequency extention, as well as high output. One day I played the movie Resident Evil: Apocolypse and during one of the scenes there was some inaudible low frequencies present. I was watching this movie at near reference level in a small to medium room. My other relevant equippment was a pair of PSB Centuri 600i floor standing speakers and a Carver AV-505 multichannel amplifier.
The Carver and the subwoofer shut down during this scene. The Carver came back on, the M&K did not. If I remember correctly the mains fuse on the subwoofer blew, and I know for certain the two internal fuses blew as well. When this occured the woofers (there are two) slammed against the magnet structure making a loud clap sound (I assume this might have been the bleed off from the capacitors). I am unsure of what caused it do that. I took the subwoofer's amp plate off, I observed the power transformer was hot enough to burn my hand.
I took the subwoofer to a local repair shop and had it tested. The shop claimed the IC output device was damaged and in need of replacement, apparently the power transformer tested good. No other parts, other than the fuses, where replaced. When they repaired it the where unsure of what fuse size to use for the internal fuses (the mains fuse is clearly stated what it should be). I don't recal if the fuses where too low, or too high of a rating. I got the subwoofer home and tried it out. It worked for a short while (probably less than 30 minutes) and stopped working again.
The repair shop has a warranty, which they honored. They replaced the IC again, and put the correct fuses in it this time. I am unsure if they retested the entire subwoofer. It's conceivable that another part could be damaged and in need of replacement due to the neglagence to find the correct fuse value the first time because it blew again after a few short days, and I don't believe I was being very hard on the subwoofer. M&K made very good subwoofers designed for high output, and low bass. I would expect a $1000 subwoofer to perform as such.
Both woofers seem to be fine, there is no rubbing sound when you press on the cones and they both work when connected to an amplifier.
Have I just been horribly unlucky and am I just getting all these low frequencies imposing taxing loads on the subwoofer's amplifier, or is there something massively incorrect with the subwoofer's amplifier? I am aware these factors aren't likely enough to figure it out, but what's the likelyhood of it being one way or the other.
Thank you in advance for any advise or insight,
Seth