throw the 6x9 away. 6x9 should only be used if u dont have a woofer in the car to make up for the lack of bass. but if u insist on using the 6x9 with the woofer... get ready for some seriously shitty bass/ sounds.

as for the monoblock. it helps to deliver cleaner power to the woofer. more stabil. and the monoblock should run cooler than a 2channel amp.

the x-over is usually used to split signals from HU to amps. 1 way for front..1 way for rear and 1 way for sub.