I lost off abit on page two but heres a thought.
Maybe you have damaged the voice coil/motor on the sub so its shorting at certain levels. (would explain the slamming of the boot kicked it into life

)
Have you got an ohm meter handy. A multimeter that measures resistance.
If so disconnect the sub.
Wire the terminals of the sub upto your multimeter. + to +, - to - for example.
Set it so measure resistance.
slowly and evenly/gently near the centre of the sub at the sides of the dustcap Press the sub cone downwards slowly.
The resistance on the meter will change but it should not go really low or to zero. If it does then your sub is causing the system to cut off as its damaged.