Why did you buy 2 subs if you only plan to use 1?
But no matter... I'm guessing you mean that your sub is 500W
RMS? Not 500W Peak?
If so, you want an Amp that pushes 500W @ 4 ohms. And you'll want a Class D (Mono) amp.
So for you, since you're using Kicker, I would stick with Kicker amps as I've been pleased with them. You have 3 choices.
Kicker
IX1000.1 (1000W @ 2 Ohms, 550W @ 4 Ohms) - Most Expensive, smallest footprint
Kicker IX1000.1 (11IX1000.1) Mono Class D Car Amplifier
Kicker
ZXS1000.1 (1000W @ 2 Ohms,
500W @ 4 Ohms) - Middle of the line, best for cost effectiveness/quality
Kicker ZXS1000.1 (12ZXS1000.1) Class D Mono Amplifier Car Amp -->This one will most likely be your best bet for cost effective/power matching for your sub.
Kicker
DX1000.1 (1000W @ 2 Ohms, 550W @ 4 Ohms) - Cheapest, Least advanced model.
Kicker DX1000.1 (11DX1000.1) Mono Class D Car Amplifier
Also, if you want you can use this calculator which will help you decide:
Matching Subwoofers & Amplifiers
