X2 on the polk speakers. Love my dxi components. Marine grade too (Waterproof)Excellent subs! Great amps! And good full range speakers. IMO go with Polk Audio for your door speakers, they are amazing for the price.
Go with these, they are a 3-Way speaker also and marine certified!:
Don't get me wrong the Diamond D192i's are good speakers but with the 83db sensitivity they will take more power to be at the same loudness as the Polk's which are 93db.
I have a 12" Diamond D6 powered by a JL Slash 500/1v2 and it has some impressive depth with sound quality that will keep any audiophile happy.