This is my understanding and how it works on my 2805.
For HT/Movies - If you have your mains set to large and your sub to LFE and a crossover of 80hz. Any freq's below 80hz on your center channel and surrounds will be directed to the sub. Anything below 80hz directed to the mains will stay with the mains, so you will be losing a lot by not directing some of that to the sub, which is its purpose. LFE+Main is different, then the LFE from the left/right mains is directed to both sub and mains. This can be good and bad, as you really should let your sub do its purpose, LFE.
Music - is different. In Stereo, Direct, or Pure Direct your sub should play any low music unless you have Sub = No set in the receiver.
