Joe90
Just for a bit of background - I have pretty sensitive hearing in the upper midrange (and minor very high frequency hearing loss)frequencies (but MANY people do).
The very pronounced forward sound of the horn loaded tweeter and midrange designs quickly gives me listening fatigue. I also used to experience that to a lesser degree on the older Cerwin-Vega semi-horn speaker designs. As a baseline comparison, to the old Klipsch horns, the M60s have a SLIGHT tendency to do the same thing but to a a MUCH lesser degree - BUT only on certain music (CDs). I am fairly convinced that it is more of the recording technique than a characteristic of the 60s driver/crossover design. Many pop/rock recordings are miked and mixed specifically for radio and/or boom box (and portable) play. Thus they are too "hot" for many good stereo systems.
Since I have never heard the M80s , I cannot speak to their sound, (though I understand they are very similar to the 60s) but I had the 50s and 60s side by side in my LR and I CAN tell you the difference between them - and the 60 is definately MORE forward (clear, clean) in the mids and slightly brighter on the very TOP end (but Hey, I REALLY like that part!) Nothing makes me smile like hearing the crisp sizzle of a high hat or a tamborine, the attack (uppper snap) on the snare drum, or the bright brassy sound of a trumpet.
I hope this helps!
Randyman
