Dave, the setting of the LFE low-pass filter is relatively insignificant, whether it's at 80Hz or 120Hz. Theoretically, the separate(as you now understand)LFE channel which occasionally contains special low frequency effects during movies extends to 120Hz. However in practice the LFE channel contains little or no usable content above about 80Hz and most is well below that. A reason for possibly setting the LFE filter at lower than the maximum 120Hz is that some useless noise at the upper end might be minimized. Others say that the full 120Hz range should be set just in case something worthwhile is there. Your choice; I'd suggest leaving it at 80Hz.

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Enjoy the music, not the equipment.