In reply to:
This is for 2 channel music in a small room.
Definitely can go with M3s.
In reply to:
they may move to a bigger room as part of a total audio/visual surround system
Again, M3s will do fine unless you have a tendency to really crank it up (and not really knowing how big that future room will be) the M50s will be an investment that will last. I believe that the M50s will give you as much performance as the M60s, just a different type of sound; classified usually as "laid back".
While upgrading your receiver will make a difference, it will be minor compared to the difference in upgrading the speakers. I had a Yamaha RX-V2090 that I bought after selling my Adcom GFA-535II. The sound was "flat", almost lifeless in comparison to the Adcom. The speakers were the biggest upgrade I had made at the time. I now have a Harmon Kardon receiver. It is another temporary unit until I can go to separates (my end goal).
At some point you will have to upgrade your receiver but don't make the mistake of making sacrifices to do it all at once. You really have to think about your end application and focus on that as your goal.
