I don't know what the M80 v3 was. Did it include the three window braces and upgraded crossover that got rid of electrolytic caps and ferrite core chokes?
The M100 has six window braces if I'm not mistaken. Also, I doubt very much the M80v3 went through the intense family of curves modelling the M100 did. So you are paying for a lot more than just hardware. You are paying for vastly improved acoustic engineering.
Craig Chase sold his Legacy SEs because the M100s sound better to him. I can't wait to get mine.
BTW, the tweeter not only sounds better but also looks very cool. I want one to wear as a medallion around my neck...lol!
