Let me clarify a few things first:

The HX2 has a MAX of 1000watts(which is pretty much meaningless) and a recommended RMS of 500watts.

If you want to give them 500 rms, you're gonna have to get an amp that will do one of the following:

Put out 500 rms x 1ch @2 ohms bridged
-you'd need two of these amps, with the coils on the subs wired in paralell and bridged to the amp and it would have to be stable to 2ohms bridged.

Put out 250 rms x 2ch @4 ohms stereo
-pretty self explanatory, again you'd need two of these

Put out 1000 rms x 1ch @ 4ohms bridged
-you'd only need one of these. You'd wired your coils on each sub in series, giving you an 8ohm load on each sub, then wire the subs in paralell giving you a final impedance of 4ohms mono. Most amps are rated to 4ohms mono so that won't be a problem, but because it's gonna need to put out 1000 rms, it will be pricey.