Continuing the role of devil's advocate, The 3808 manual states that "..speakers set to small, sound below the crossover frequency is cut from the sound output. The cut bass sound is output from the subwoofer or front speakers."
I take that last 'or' to mean if the front speakers are set to small(which makes all speakers hooked up to the receiver small, as long as there is a sub) then all the bass below the crossover is sent to the sub making the LFE+Mains setting redundant when front speakers are set to small, as all the LFE and Bass for all speakers is now sent to the sub because of the small setting.
The LFE+Mains setting allows you to use a crossover point for the mains when they are set to large preventing the doubling of all the bass frequencies.
