Deaden the door and sealed it off as others have said.

The 8inch sub is a bad idea.

You can try crossing your subwoofer higher like to 100hz or so to see if that helps until you deaden\seal you doors. Might want to try to lower your xower point on your 6 1\2 to 80hz.

The most definitive factor I find for great midbase is the song you listen to.... some have awesome midbase, and others dont.

 

^^source material is the most influential part or a good system...a poorly engineered track sounds bad on any system!