Let him give you the long story but I can offer my short one. LFE is the .1 channel so it has nothing to do with the re-directed bass from the other 7 speakers that are set to small. If the contents (e.g. SACD 5.0) have nothing above 80 Hz, then setting it to 80 or 120 Hz makes no difference but if there is content above 80 Hz (apparently in some cases there are things >80 Hz) then setting it to 120 Hz will allow you to hear it.
That is true, I guess we have to ask the authors why they allow contents of frequencies that high in the .1 (LFE) channel.
By the way, if you ask Audyssey, they would likely suggest setting LFE to 120 Hz.
In that case you must be able to set the LFE effects on that receiver, separately from the redirected bass from the other speakers.
At least on mine you can't, and the design for the low pass of the LFE/and bass from stereo sources is 60 Hz.
In that configuration everything seems to work fine.
I have just done some checking on pro sites, especially about mastering.
DTS only supports up to 80 Hz on the LFE channel, Dolby up to 120 Hz.
The general consensus seems to be to cut off the LFE channel between 60 and 70 Hz.
For multichannel music the advice is to leave the sub channel blank, otherwise there are serious phasing issues between the LFE and other speakers. That is the way all mine are.
However customers get upset when there is no sub output, so if the studio client insists on something on the LFE channel, the the advice is to put some very low bass at low volume on the LFE channel.
It seems the best approach for music is still integrated full range speakers.
That was the consensus at a recent AES meeting in the Twin Cities when we got around to discussing this issue.
However delivering the LFE signal into full range speakers takes some thought and is a challenge.