How do you figure that the PA2000 is more powerful than the A1400?
If you are really worried about your son maxing out your system and destroying it due to clipping, then take the maximum rated power of your Energies, double it, and that's the amount of power you should look for in an amp.
As to what amp sounds the best, audible differences may arise from the distortion by-products. Some have more odd harmonic distortion components and others may have more even harmonic distortion components. Now as to whether or not these differences are audible, I don't know. I haven't spent any time doing any comparisons.
Remember too that the more sensitive the speaker, the louder it will sound with the same power input.
