I haven't heard the M80s, but I can't imagine needing 2 of those crystal clear titanium tweeters on each speaker. Everyone knows these speakers need room to breathe - in particular I think the tweeters need room to breathe. If the M80s are no "brighter" than the M60s then go for it, but with hardwood floors and 15' of drywall on all sides... I'd play it safe and go with M60s and the most monstrous sub SVS makes.