"If you want the perfect power amplifier for pair of Club S115s with a 500-watt program rating, for example, the P5000S with 500-watts per channel into 8 ohms is the obvious choice." Seems pretty conclusive.
There is a useful discussion here:
...which might inform your choices. It seems a pity not to use the built in power amps if they're working. Keep the tops stereo and sum the bass (I doubt if you'd notice the difference, I didn't).
Ohm's Law states, "Your PA isn't as powerful as you think it is".