You won't destroy anything. The amp's 2 common posts are connected together already, as are the common leads of the 2 sections of your crossover network.
There's nothing wrong or dangerous about doing something like this other than wires fraying or connections coming loose and shorting the amp out. All you've done is manipulate the impedance that the amp sees as part of the total load. If this gives you the sonics that you were looking for, relax and enjoy the music : ) Sean