I'm not familiar with many of the pieces you mention in your post but on my 600, the Darla scene and U-571 does not lack any punch, period!
It is next to impossible for me to tell though what's mid-bass and what's sub-bass on special effects passages like these. A better indicator is music. And I think it boils down to the fact that there isn't much mid-bass and our previous subs simply boosted the mid-bass to make some boom boom.
I'm wondering now if you have your fronts set to large or you have your receiver set to direct mode and you are getting some cancellation in your room as a result of bass from your 500 and your fronts.
