Jeremy, the most common suggestion for a basic crossover setting is 80Hz, which THX and others found to be a good compromise, being high enough to take a significant load off the speakers and the receiver driving them, while not being so high as to make the sub easily localizable.

If Audyssey is set up properly(note for example the hints in the Audyssey and Onkyo 705 threads on AVS)it appears to be useful for the majority of users.

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Enjoy the music, not the equipment.