There is a bit of conflicting info being provided here..

An amp designed to run a sub should be 1channel and mono. Should also include a gain control and low pass filter.

You can bridge a 2ch amp to run 1 sub, or a 4ch amp to run 2 subs, but amps designed to run mid/ high speakers usually feature a high pass filter and dont behave the same as a mono amp designed to run a sub.

Best advice is to get 1 decent quality sub, and decent quality amp.. sad to hear you have already purchased the xplod, I wouldn't recommend them.

Try and get yourself a monoblock amp to run the sub, higher the RMS rating, the less work it has to do to produce a clean signal.