Typically ther is no crossover setting just for the LFE. LFE is a discrete channel of information and the recording engineer would have only recorded "low frequency effects" onto that channel. There is no need to do anything to account for this, other than set the subs on-board crossover point to the highest possible setting. Your receiver will send all of the LFE info to the sub, plus the under 80hz info from the surround (probably little to zero <80hz info on the descrete surround channels).
Enjoy,
TIC
Enjoy,
TIC