Right now you are just saying "this fking system *****" But your not really giving us more in depth details.
turn down your subsonic filter, 3/4 is a little bit high your practically cutting off almost all bass frequencies. Make your head unit Equalization to flat turn the subsonic filter down to 1/3.
Throw some mdf wood blocks inside the box. It'll make the box smaller and tune it higher.
Do you want lower bass? do you want punchier bass? Does it sound bloated, sloppy and uncontrolled? Or is it not outputting any appropriate level of volume? Pinpoint your problems if you want them solved.
Where did you get the box design from again as in who told you to make it that big? Those hds 200s run better on 1.5 to 2.0 cubic feet, its not a monster sub where it needs THAT big of a box. That box is more suited to an hdc3/hdc4.