It is confusing (understandably, because Denon's wording is confusing),and my interpretation of the above two statements makes them contradictory, so I have a hard time answering you!
But let's put it this way:
1) Mains are small - it doesn't matter whether this setting is on "LFE" or "LFE + Mains", the sub takes over all content below the crossover.
2) Mains are large -
If "LFE", the sub will not play the "main signal" (like typical music) below the crossover (it only plays LFE content).
If "LFE + Main", the sub will play music below the XO (in addition to LFE content).
I did screw up part of what I said:
My last statement (in bold) is incorrect in the sense that if mains are set to small, it doesn't matter whether the sub is LFE or LFE + Main.
I'm going to get specific and a little redundant just to make sure I have this hammered all of the way out...
The correct statement is the "small" setting ignores the LFE/LFE+Main setting. Look at it as Small/Large comes before this sub setting in the decision tree!
This is why I don't like Denon's wording! The LFE/LFE+MAIN control is a sub control. It does not control what goes to the main, only what goes to the sub. If the speaker is set to "large", it gets the full range signal no matter what... if it is small it doesn't get the full range signal. We only "toggle" the main signal
to the sub on and off (but that is only when the mains are large)
It doesn't seem that complex, but it sure does manage to get confusing!