I second John. There really is hardly any difference between the new and the old receivers especially if you like the way it sounds now and you're not experiencing any problems. The power required by the M3s to play at audible volumes would be the same irrespective of which receiver you have.
I have the M3s myself and I used to power them with a Panasonic receiver that was new at that time. I then tried powering them with a 7 year old battered (cosmetically) and used receiver. There was no difference in the sound. I currently have a custom built amplifier and there's still no difference in the sound except that it plays louder. IN fact, I have it built with minimal internal wiring, 40,000 mfd capacitors, all gold plated contacts (even the switches are gold plated), 7 inch toroidal transformer and the ability to play down to 3 ohms comfortably. But there is no sound difference at all. In fact, my wife and I were expecting the earth to shatter the day we got this beast home. But nothing happened. It plays clean and loud just like all the others.
So if you're happy with the sound, there's really no financial justification in moving to a new receiver.
