The discontinued Electron Kinetics Eagle 2 has superb grip and power in the bottom end. Unfortunately there are none for sale right now, but they do come up from time to time, generally in the $400 ballpark.
In the meantime, you might try wiring the drivers in your sub in series. While the wattage output of your amp will go down, the damping factor (control it exerts over woofer motion) will go up, and you may find it's a net improvement.
In the meantime, you might try wiring the drivers in your sub in series. While the wattage output of your amp will go down, the damping factor (control it exerts over woofer motion) will go up, and you may find it's a net improvement.