Yeah, I don't have a M-CH setup, so the loss of 5.1 hasn't been a factor for me.
Right now I've been comparing the setup of two left bookshelf speakers and two right bookshelf speakers to your standard 2-CH left/right setup. The motivation to do this is due to the room...not the benefit of multiple bookshelves over floorstanders.
Wasn't sure if there's a way to logically add in (amplify) a few more bookshelf speakers on each side. I guess we're thinking "wall of sound".