I couldn't wait 2-3 months, so I took the leap of faith and bought the PM-3. I currently have the Sennheiser HD600 and B&O H6 at home.
What people say is true. The Oppo PM-3 is a beautiful, well-made, high end headphone. What's also true - as many have noted - is that the high end is rolled off a bit. For me, that kinda spoils it. If the high end were as great as the rest, it would be perfect.
It does have a very balanced feel, a very full, rich sound. Definite quality. Of all my cans, it probably has the best, most realistic bass. The B&O H6 bass is stronger, but a bit exaggerated. Since the PM-3's highs are less prominent, your attention is drawn to the bass much more. Male vocals also are rendered very well, with just the right amount of bass and midrange. The soundstage isn't very wide open, but that's to be expected with closed cans. The earpads are very comfortable. Soft leather, just the right size and shape, no bigger than necessary. I wish the H6 had cups like this.
Everyone has sound preferences, and I'm more of a treble-head than a bass-head. And after extended listening with the PM-3, it felt boring and dark. Then I would switch to the HD600 or the H6 and the music would come alive much more. That's just my preference. The PM-3 probably IS worth $400, but I'm not sure if it's worth MY $400. For that much money, I want to LOVE it, not just admire it.