The RMS value is the sustained wattage they can handle, and the peak value is the peak wattage they can handle. A true sustained 500 watts is a LOT to deliver to one speaker. Basically, if you were looking on a graph, at wattage delivered, over time, the RMS value would be a line that represents an average (of sorts... technically the Root Mean Squared) of wattage over time, and the peak would be just that, the peak wattage value reached, which in your case should not exceed one kilowatt. This is my basic understanding of it, at least.