Welcome Jesterx!
I really don't think there is a wrong answer here. The Yamaha is more than enough in your current room, and you probably wouldn't hear a difference changing it. That leaves money to buy the highest speakers you can afford now. To me, this would be the way to go. Or, if you did opt for the M3's now, they can always be used for surrounds later.

Shawn

Epic 80/600 + M3's + M3 Algonquins + M2 Computer + EP125
I think I'm developing an addiction.