Is this a good idea? If I was to use Mission M51's as rears and, say, Quad 21L's as front (with matching Quad centre). The reason I ask is because I want to upgrade my front speakers to floorstanders and use my existing M51's as rears, I don't want to get rid of them since they are perfectly good speakers. Or would my choice of front speakers be restricted to something that matches sonically like something in the M5 range. I know this is technically quite possible but how would using different brands of system in a HC setup effect the sound field?