Distortion doesn't really apply to ohm rating, at least directly. (an 2 ohm setup can sound just as clean as a 1 ohm or an 18 ohm setup). Just pay attention to stability and power ratings.
Your Dual voice coil subwoofer is basically two subs in one. They can be wired in parallel (not daisy chained, but both coil's are wired straight to the amp). This will cause your amp to "see" a 2 ohm load. At 2 ohms, your amp will deliver 400 watts (probably more if you look at the "birth sheet" that comes with the amp). Your sub is rated for 500 watts, so this is well within spec. If anything you could use a more powerful amp, but 100 extra watts would barely give you 1 more dB.