My system is a mix of several different speaker lines. The front three are all boston acoustics. The back three... well, I don't have three yet, this is the reason for the question. My back 2 are JBL bookshelf speakers, which I like. They recently replaced my old main JBLs I've had since the mid 80's which were the rears. With a new 6.1 system how important is it to have the balanced or matched set of speakers. I've heard that the front's and back don't need to be matched, but what about all three rear channels? While on the subject. How important is a true center channel speaker? Could a third bookshelf work in place of a center channel?