Just an update around a month of daily usage later...
I am in love with these headphones. Is there a magical Ultrasone fairy that helps these headphones improve over time? Absolutely. For almost every headphone out there, burn in would seem to be a complete myth. These are a striking exception.
Now, don't get me wrong... the overall sonic signature doesn't change a lot: these are bass and treble cans with recessed mids. Nothing will change that. Also, these headphones will exaggerate the flaws in anything less than pristine source material so if you mainly listen to youtube, you might be disappointed.
Originally, my complaint with these headphones is that the treble was painful and exaggerated to the point where I couldn't appreciate the bass. This is what has really changed. The treble is still exaggerated... but now it's pleasant and 'crispy' rather than the ear-drum exploding sibilance I had to deal with before.
I was hesitant when purchasing these because when people said it was a 'bass monster' I was afraid I'd be getting something akin to a ghettoblaster for my ears. The bass is really quite different. It's incredibly detailed (I didn't even know it was possible for bass to have that much detail) and has a massive range (there's not a gap between the very low frequencies and the low frequencies). If you close your eyes, you can feel something akin to being in a club with a high end funktion one sound system.