If the sub has a lot of oomph, making things vibrate is what they do, which is accomplished by moving large volumes of air, not passing vibrations to the floor. My Hsu is carefully decoupled from the floor, but from the basement, a movie like the Dark Knight still sounds like a thunderstorm on the second floor. Walls that filter out a lot of highs, will be transparent to lows. Once you bought them a subwoofer, you opened the door; now it's an issue of agreeing on an acceptable loudness.