I actually did lots of reading on the Valhalla, and found that it was on the bright side(a no for me) and that it wasn't that much of a jump from something like a Magni, which is in the same class as a E09K.
If i was into treble energy i would probably be after it though... the aesthetics and build quality alone are superb.
My bad. I meant the Vali. I agree that the Valhalla was too bright with the HD600 and I thought the Magni was too, while the E09K was too dark, though it paired up better with the HD600 than the HD650. The Vali I consider a jump above both the Magni and the E09K.