To my ears the treble is certainly there on the pm-1. My hd650 is certainly a darker hp when it comes to treble presence. The hd800 is certainly brighter and more treble energetic than than the pm-1. But I don't feel that I'm missing and details or any of the music when I listen with the pm-1.
It's a well executed design functionally, aesthetically and musically. It doesn't punch as hard as the lcd2, but it puts you in the same neighborhood. The overall sound signature is very cohesive and blends well. It just sounds "right" with nothing wonky or strange about it. Good speed on complex music and the decay seems quick.
It's an interesting hp. I can't think of other flagships that could be driven so easily with maybe the exception of the d7k. Some might turn their noses up because it doesn't need a powerful amp like the he6...not me. I just sit back and enjoy the music with this fine hp.