How to set up sub?

 Problems setting up sub not enought clout expecting more from the five star quad sub. Have i set it up correctly ,amp onkyo 606 qed sub cable first time setup with audyssey 2eq gave me readings of 150hz for front and centre 80 hz for rear and 100hz for sub. -6db for centre and -7db for front and rear with -15db for sub. I tryed changing the sub to 70 hz and 90 and 120 no difference also the the -15db too 0 bit of a hum when doing that just wandering if the amp is powerful enough. sub is on volume 99 and doesnt really explode seems to be a bit bassy during speech as well and when the explosions happen in black hawk down does not really delivery any depth. Any help please.