kicker L5 box and sub question with (900watt) amp?

[Michael]

I have a set of kicker L5 12 in sub with the kicker box and i cant get it to sound good in my car i guess i just payed all kind of money for a indash and subs and apm and wires and all kinds of Sh** and i just want it to sound good will some one help me please if i push my box all the way to the back of the seat it dont sound good but if i scoot them up sum they sound better and i just want them to beat my head off and i have a 98 buick century and all i want is it to sound good tell me what i need to work on getting and or what do i have to do to make it sound better with what i have allready i have spent over a grand and a half prob more so dynmat an every thing PPPPPlLLLLLEEEAAASSSEE HHHHEEELLLPPP and no short answer give me something i can do thanks it just sounds like the bass isnt hitting like it is suppose to and i have hurd of these speakers b 4 and they HITTT Hard so thats why i chose kicker please help fast......