I have a buddy that put his center channel in the rear in a 6.1 surround set-up. I think that it sounds great, and adds plenty of envelopment. We placed it vertically behind the main seating position.
While some may warn about a phantom signal comign from teh rear and sounding like it is coming from the front, I say, what the hell, give it a try.
Consider this: You are getting the 150? Deal's done? Then there is no harm in trying the 100 out as a rear for at least a little bit. If you find that it please you, then Bob's your uncle, and we'll all go about our hapy lives. If it doesn't make you happy, there are other alternatives (new 5.1 system in another room, selling it on eBay, yada, yada...). I would suggest that you give it a try and see what you think of it. There's no harm in trying.
