The LFE channel isn't supposed to include pre-crossed over audio. Basically if you lose the LFE, you don't lose anything important. It's for Effects: earthquakes, explosions, etc. That doesn't mean there can't be non-effect low frequency content in the mains.
It seems that many receivers when the sub is set to None, it mixes the LFE content into the mains. That used to be disallowed, but appears to be common place now.
So something you may want to try. Don't disable the sub channel in the menu, but leave the mains set to large (don't use the plus mode). That'll at least keep the LFE out of the M80s.
