After reading numerous articles suggesting the best voice dialogue is to be had from the main left and right speakers, assuming they are correctly positioned so that the viewing position forms a sort of equilateral triangle with the speakers and screen directly in front.
You do this by indicating in the AVR speaker menu that there is no centre speaker. I tried this and found that instead of hearing the voice of the central character(s) split between left and right as is the case when you view a show but select stereo as the listening option, the dialogue genuinely appears to come from a central location, just as it would with a centre speaker located there. Needless to say my centre speaker now sits in the garage gathering dust. The clincher to doing this is there's little doubt that my mains kick out better audio than the smaller centre can, despite them all being Kef's.