Paul,

The depth charge scene definitely shakes my couch with the 600...and my entire upstairs. Did you check to make sure that the frequency cut-off knob on the back is set to "by-pass"? Do you have "sub-woofer on" in the receiver?

Don't get worked up about the 30 day return deadline. Call Axiom and tell them that you are having these issues. I am sure they'll work with you and extend the deadline.