With a steep LPF slope and LPF frequency set as low as yours this shouldn't happen. It sounds like your main speakers may have sufficient output in the sub/mains overlap range to cause a broad peak in the frequency response. Perhaps room gain is contributing to produce excessive bass in this region too (typically, room gain will be down around the 30hz mark depending on room size). The only way to know for sure is to buy/borrow a Rat Shack SPL meter and measure the response in this area.
If this turns out to be the case, you can reduce output in this area by using HPF's on your main speakers. Unfortunately, bass traps are unlikely to do very much at frequencies this low. If your room is a sealed room (ie. no openings to other room or stairways etc), try listening with all doors open and see if this reduces the problem.
