Ray, setting the crossover at 80Hz instead of 60Hz means that the sub will be more responsible for 60-80Hz and the speakers less. 80Hz isn't necessarily the "right" setting, but it's a good compromise, as determined by THX and others, being high enough to allow the sub to take a significant amount of the lowest bass load off of the speakers, while not being so high as to make the sub easily localizable.

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Enjoy the music, not the equipment.