The IX500.2 will deliver 250W rms x 2 @ 2 ohm, so each 8" Icon-8 would net 125W. Although the Icon-8 will handle more power, 125W to an 8" coaxial is good solid power, especially when there will be 2 pair. If buying the speakers and amp as a package, the HT2 would top of the list as an amp, but since you already have the IX500.2, rock it.

The IX1000.5 will do perfect with your 3 pairs of in-boats.