I can see it's clipping. It's hard to tell how loud that is via the video clip, but it sounds way, way lower than what I get out of my pair.
Let's put it this way, we were watching Dune the other day at close to reference levels and my amps never clipped. And that was FAR more bass and far more volume than what I heard in your video clip. Which leads me to believe that there's a problem with the setup.
2 things I'd check - 1st, are you using the RCA connectors or the speaker connectors into the subwoofer amps?
2nd, put on something with crazy low bass at high volume and look at the woofers. They should be moving back and forth a LOT. Like an inch or more. Verify that the top and the bottom woofers are in synch (ie, both move forward together and both move backward together).