With three D2 coils you'll end up with either a .33, 1.33, 3, or 12ohm load...I'd go with the 1.3 ohm load and just get a soild amp that does it's max power at 2ohm(kicker ZX2500.1 would be great).
i also hav the kicker sx900x4 on my highs and i dont think they are loud enough, i jus want a good sound but it doesnt hav to b competition level' i hav 4 6x9's, 4 6.5's, 2 4x6's all pioneer and 4 kicker tweeters and they arent too loud, do i need to add more wattage