Direct should directly send each channel's audio to that channel. So for CDs there'll be no sub-woofer activity. But for formats which have a .1 channel, the sub will get some information, but only that which is encoded as LFE. So that means all your other speakers will be forced to play full range for any content which is on their specific channels.
Personally, even with music, I want my receiver crossing over the low bass from each channel to the sub were it is handled better. So I don't use any "direct" mode.
I give up ... which mode do you use?
