About 60+ hours into burning in my new DT880/600s and its odd how my perceptions of the phones are changing - for the worse. Right off the bat, when listening to a group of recordings that I consider well done, and that I know well through both my big rig (featuring Apogee Duetta Signatures) and my previous headphone setup (either Beyer DT-990/600 classics or Etymotic ER-4S), the phones sounded terrific - if a trifle hyper-detailed (which, given my comfort with the classic Etymotic sound, was not a big deal).
Now, at about 60+ hours in, when listening to more run-of-the-mill orchestral recordings, my impression is of a persistent grayness. Not sure how much of this is a reflection of the phones accuracy, or a lack of tonal compatibility between the Schiit Vahalla's strengths & DT-880s weaknesses, or of my ultimate preference for a detailed yet slightly more euphonic, forgiving phone (maybe the Sennheiser 650) - given the reality that many 1950s-1990s orchestral recordings are poor-to-average sounding to begin with (too many microphones deployed, too much mixing, etc.).