I may have read your post wrong but I thought the centre channel comprised of stripping out the differences and only allowing through what's common to both channels. Otherwise you'll get all those nicely separated signals coming from the centre of the soundstage and stuff like vocals (which are usually placed in the centre) removed completely. This is how it works isn't it?
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Marcus 32 gig MKII (various colours) & 30gig MKIIa