Well, I AM at a disadvantage since I have never heard the M80s. So I have to take your word on it, however, a response from Ian or Alan on why this is/may be so (considering the effeciency rating for the speaker) would be enlightening.
In response to your comment about the woofers wanting more power: Indeed, the low frequencies require much greater power to be reproduced at loud levels, but different amps can truly have an effect. And I am not criticizing your H/K amp. But this is an example: Many years ago, I had a 90W Sony integrated amp that had what the company called a "pulse locked power supply", that was supposed to be "superior" the the big heavy toridal (sp?) core PSs used in most other quality amps. Well - it wasn't! That amp had NO BOTTOM! It was great on mids and highs - but that was it.
Well anyway, thats my rambling for now......
Thanks canadian_guy for your observations!
I may have to rethink my amplifier purchase for my possible move up to the M60s - if they are anything like the M80 in power wants/needs.