My Onkyo receiver sets my VP180 to 40hz every time I've run it. Some time I leave it, sometimes I bump it up to 60 or 80hz. Like Randy states, that is OK, wit Audyssey because you are basically removing calibration extension in the lower frequencies. However, if it sets something to, say, 80hz, and you drop it down to 60hz, Audyssey hasn't done any room calibration down between the original 80hz and your new 60hz setting.
M60s, VP180, VP150, QS8s, SVS 20-39PCi, HTPC, JVC RS45, Onkyo TX-NR709, Shakers