PM-1 measurements vs LCD-X and HE-6 : http://stereos.about.com/od/Measurements/ss/Oppo-Digital-PM-1-Headphone-Measurements.htm
Nice find, pfillion! Thanks!
At first glance, Brent Butterworth's charts imply a disappointing treble response, but reading his analysis, it seems I have no clue how to interpret these plots!
His analysis of other measurements indicate less than "perfect" results, but nothing alarming, in my opinion.