Ok here is a bit of information for amps and power. First the rated power is always peak on any car audio amp, which is what the ones you linked are. rms power is normally 1/4 or less than the peak rated power. Second the power is rated for specific impedence, or the ohm's of the speakers. If an amp says it puts out 200 watts into 2 ohms, then it puts out 100 watts into 4 ohms and 50 watts into 8 ohms peak. Your rms watts will be 1/4 of the peak of 2 ohms 50 watts peak, 4 ohms 25 watts, and 8 ohms will be 14.5 watts. Now seeing as your speaker should be 8 ohms you want an amp that will put out high wattage at 8 ohms. The one I linked above is designed to do just that. It will give you everything it has at 8 ohms. Over-driving a speaker will shorten its lifespan siginificantly. Using an amp with more rated wattage than a speaker can handle will destroy said speaker real fast.
A stereo amp like those that you linked above will like Stangshcky12 said split the wattage between the 2 channels thus giving a lot less than advertised wattage. You will need a monoblock amplifier with no more than 50 watts peak (I had no luck finding any that were that low power). Even though yur speaker says it will handle 50 watts it most likely means peak wattage and not rms wattage. rms wattage is what you want to look for, an amp that has no more than 15-20 watts rms will be more than enough for your PA speaker.
