David, lots of discussion on this since last night, but you discovered the reason for the change in bass that you heard when switching from "LFE" to "+" with speakers set small(which generally is meaningless, as I pointed out before): the cause was that you were in direct mode, which doesn't allow any processing to send low bass from the mains to the sub, and since there's no LFE on CDS, of course, the sub gets nothing and the M80s were handling all the bass alone. So obviously don't use direct mode, but continue to use the basic small and LFE settings.
Although a couple of the posts stated this backwards, with large and "+" set, it's the frequencies below(not above)the crossover frequency set which are doubled in the M80s and sub.
As to why the Denon even allows the small and "+" settings which are inconsistent with each other to be shown together, is unclear. Some other Denon models, e.g. the 1905 that JonHan mentions, don't permit the setting.
