I wanted to make a comment about the amp. Unless you enjoy listening to music at psychotic SPL levels in your room or you want to use these for DJ'ing or something, you don't need anymore power.

My bass reflex 2-way's are not exactly like four pi's, but they are quite similar. Kappa 15lf with a PSD2002. Sensitivity is only about 95 decibles. However, with my amp applying at most maybe 50 watts, these things just scream. I think you'll be happyu with a most amp. :)

Adam