If you do decide to move to surround sound, I'd suggest adding the center channel last as you may find you don't need it (so long as your processor can direct center channel dialog to the mains).
2-channel vs 3-channel/5channel
I have been enjoying some B&W N802s for movie watching in 2 channel. A real pleasure. My question is, will I gain a lot of enjoyment by going through the complication/pain of setting up 3.1/5.1 or is 2 channel "enough" for movies.