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.
yes, most modern receivers, if you set the sub to "none" it will automatically set the front L&R to large and send all LFE or any crossed info from surround & center channels to the front L&R. so until he gets a sub, like you said, select yes that there is a sub. also for the front L&R channels he can adjust the level for each channel, that will help with too. also in most modern receivers in order to have double bass, your front's have to be set to large or full in order for that to work. another thing i found that's interesting on most Onkyo's is that if you have the speakers full (and your only listening to 2 channel analog or you only actually have 2 speakers) you won't have a sub because the receiver will send everything to the speakers. you actually have to back it up to say 40hz, then it will automatically allow the sub to function and you will have 2.1 then you can cross over to the sub.
