I think just about anything, within reason, will drive the M60's just fine. One of the first things I noticed when I got mine a couple weeks ago was just how effortlessly my existing equipment was driving them. They are very, very nice btw.
I wouldn't worry too much about trying to future-proofing a reciever to someday drive M80's. By then, you'll probably want a move to an up-to-date receiver with 4D
A better approach might be to get a two channel amp, or a pair of monos when and if you get M8o's - and use whatever power you have in your reciever to power center and rears.
It seems like recievers are becoming somewhat disposable like computers. New, can't live without them, technologies are relaesed in every tradeshow, where amps are amps - they can provide good service for decades.