Yamaha tends to be bright so I would match with a speaker that will calm this effect unless, of course, you like it bright. Only your ears can tell you what you like. What speaker options do you have in your area to listen too? Athena Asf, Wharfedale Diamond, Tannoy Fusion, and Polk Rti come to mind initially in that price range
Check out the Paradigm Monitor 7. Lists for $699 and store prices should be no more than$625 at most. Perfect match with Yamaha. You need to keep in mind that Paradigm's are not shielded so if you need that you will pay about $30 or so more.