I currently own a crappy D-Box David 250 from Costco (I can't afford an SVS atm). There are two knobs on the back of the sub, one for volume and one for X-Over. I am having no problems calibrating the volume on the sub but how the heck do I set the x-over to 80hz ? There is no label or anything on the X-over knob that states what hz the crossover is set to. I have my Denon 1803 set to crossover at 80hz and would like to match the setting with the sub. Any suggestions would be greatly appreciated!!