If you have 2x dual 2 ohm subs, you put both of their coils in parallel, so that you essentially have 2x 1 ohm subs. You then series them up so that electrically they look like 1 2 ohm load. The Kicker zx 750.1 is made for 750W@2ohm. The 10" CVR is made for 400WRMS each, so you're running them at 375W each in this configuration. As for the rest of your setup, it's probably your install and box. Then again, what is loud to you?
Edit: I got tired of harassing him, so I decided to help. Now, buy one of my amps. I will be having 2 PA 3000d, 1 Planet Audio P2550, and an Orion 2500d up for sale soon. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Possibly more.