Darren, the first thing is that you're attaching far too much significance to speaker maximum power ratings. Theoretically they represent a continuous power input which a speaker could handle without being damaged; in home use these things are pretty much meaningless. Speakers such as the M80 and M60 will use about 1 watt at a comfortably loud average listening level and split-second peaks might use up to 100 watts or more, but there's no "matching" of the speaker and amplifier maximum power ratings needed(a thousand watt amp isn't going to endanger the speakers; the extra power would simply be unused and meaningless). There's also no need to think about a lower impedance speaker "pulling" more power from the receiver; if the 4 ohm speaker isn't less sensitive it doesn't use more power.
Your receiver should be fine at this time and the M60s should give you excellent sound in your present room and in their future location.
