Exactly what Mark just said , their ment to be in a ported enclosure

 

it sounds like you might have a phase issue between your 8s and 12s try putting both 12" woofers the opposite phase and you should be able to have your filter set to 60hz personally i don't set sub filters past that usually there around 50hz and your mids should take care of the rest depending on the speakers your running

And yes Luke99 is right they look like they would be a way better ported woofer I would run one woofer ported off that amp i just plotted that woofer in a 2cuft box a 3x6x16 port would play quite nice down to 35hz