My K is powered by a Rockford Fosgate 150S stereo 37.5 x 2 @4ohms or 75 x 2 @ 2ohms. My sub is wired in a bridged 2 ohm load, so the amp is givin 158wrms x 1 @ 2ohms, as is the max on the spec sheet. So 158wrms pushes my sub. I listen to it very very very loud a lot, so honestly I wouldn't bother going up to the O or especially A unless you are really into SPL. As for the displacement, do you mean of the back of the sub in the box, the amount of air moved by the sub, or the size of the box interior? On ED's site, they have blueprints for different box types. I built the small sealed box on the site as per spec and it performs very well.
