What is the fundamental difference between a dedicated center and a left/right bookshelf? Why do some centers have two drivers while others have one? And if two drivers are better than one, why is it that some manufactuers higher end centers only feature one driver while their lower end models have two? Furthermore, B&W recommends the LCR 60 to match with my 601s3's. Why not just use another 601, turn it on its side and use it as the center? Just a curious thought. Thanks