u cant really know if your amp its clipping even if its sounding bad.. the only method to see if ur really clipping your subs its to the output of the amp with an oscilloscope
If you set your gain to your amps output at 12 volts, it won't clip. If you used the amps 14 volt rating, it will. (this all is assuming the amp has an unregulated power supply, in other words power output varies with input voltage)