I really hate to tell you guys this : But my ATH-M50s now have 440hrs of burn in on them, and after not listening for the past two days, they have changed even again !!! Good news is they are getting MUCH better in the mids and highs, more coheshion ( sp ). Bad news is, although the bass is gaining in great levels of resolution, tone, and character ,... it is also getting slightly more prominent ..... The Kees mod is definitely needing to be tried next.
Also, while these phones are VERY fun to listen to on dynamic music, they never let you forget they were designed to be studio monitors first. They are very revealing of the quality of source being used, and excell with better sources.
Lastly, regardless of how easy they are to drive, my P-51 Mustang made a completely different set of cans of them, and they REALLY shine with this amps extension and neutrality.
HTH