1 coil per channel will be fine, make sure the crossovers on the amp are off or set all the way down hopefully you can turn them off, if it happens to have a subsonic you want to set that around 20, lower will allow lower frequencies to play on the sub which may bottom it out, but unlikely with the kinda power you're running. If any of the subs don't move as much as the other check for loose wires and the polarity as the coils could be wired opposite of each other on the sub that is having issues.
don't bridge the amp and try to run 2 ohms, you will easily burn up the transistors as they will not be able to handle the current, and the amp is a class D, I don't even have to check, almost all cheap amps are, class a and b amps have efficiencies less than 60% and are ideal for SQ, mids and tweeters.