In response to mbfleming, who bottomed out his 'loaner' Sub 1 during the cave emergence scene in Iron Man:
I finally got around to checking this scene. All speakers (sub included) are Audyssey MultiEQ XT calibrated, in a big (~7000 ft^3) room. I tried at -20, -10, and 0 on the volume. I usually watch movies at -10, which is quite loud. At 0 volume, I turned off the external amps running the speakers to avoid hearing damage, so only the sub was running.
Although dozens of things around the room were rattling (fireplace, sconces, the projector, glasses in the bar, etc), the Sub 1 exhibited no audible distortion/bottoming out/whatever.
In fact, I hooked up my Kill-A-Watt meter to the sub, and the peak power draw from the outlet during this scene was only 350W, despite the absurd bass that felt like it was ripping my house in two. After about six runs through that scene, the plate amp was barely warm. The Sub 1 is capable of pulling about 5 times that power from the outlet, so that was only the tip of the iceberg.
So mbfleming's Sub 1 was either defective, his room EQ ate up all his headroom, or the distortion was coming from something else in the room rattling (rather than the sub itself).
Unless you run your sub WAY above reference level or your theater is in a gymnasium, I don't see how any Blu-Ray film made to date could max out the Sub 1. Just because the Sub 2 is even more powerful, don't discount this beast.