On the Audyssey website it states the following about the LFE crossover setting:
LPF stands for low pass filter. A crossover requires an LPF and an HPF
(high pass filter) to work together. The LPF allows the low frequencies
to "pass through" and they are sent to the sub. The HPF takes care of
the remaining higher frequencies and they are sent to the satellite
speakers.
The LFE LPF is an entirely different thing. It's not a
crossover (because it doesn't come with a corresponding HPF). It is a
filter that is applied only to the separate LFE track that is found in
surround content. This low frequency track is added in the mix by the
people producing the content. It is limited to 120 Hz and below and so
the LPF LFE should always be set to 120 Hz.