"I suspect those processors also send .1 to speakers designated as large or full range if no sub is specified in the menu"
May or may not be true; I was pointing that out so the OP could check for sure. I was thinking along the same lines as Kal, that there is no reason for that to be true, unless there is some quirk in the DSP or bass management software that does not route the deep bass to the fronts in 5.1 if there is no specified. Of course since the OP never specified that he was using a sub or a center, it's also possible that in 5.1, he was NOT routing the deep bass or LFE channel to the fronts. Another possibility is that he had (mistakenly) identified the fronts as small or otherwise fooled the bass management software NOT to send the full range signal including the LFE channel, to the fronts. I will admit that Kal is WAY more knowledgeable about multichannel than I am.