Iron Man was the "movie" that caused my single sub so much distress, I got concerned and turned to this forum for help, and learned I could use a setting on my Onkyo 906 AVR to set LFE to -10, as adding a second subwoofer in my small apartment seemed like a "bad" idea, neighbors etc. It was not so much the "case sequence" as was the prolonged "taking off" when he goes into flight, the rumbling and the physical movement of my 12" subwoofer driver was SCARY, not sure if it really bottomed out as it seemed to hold it's own, but some of those movie scenes lasted longer then I "thought" the subwoofer might last. Since much of the SFX, bottom end is in the LFE channel, I was able to bring it under control with a simple setting in my AVR, for those in home settings, with NO neighbors, adding a 2nd subwoofer is a NICE option, but there are other ways to avoid blowing up the sub.
Check that your AVR has not turned on "night mode" and you have the gain boosted to compensate for that. Something about the way the movie is (mistakenly) coded requires me to manually turn night mode off. I sill needed the additional displacement, but this little quirk didn't help.