I agree about the long break in period with Metrum's Onyx DAC. I did not believe that it would take 4 weeks, until I experienced it for myself.
My Onyx DAC has around 280 hours playing time at this point. I have had the DAC for 4 weeks, playing at about 10 hours a day. I leave it on 24 hours a day. For the first time with my system, the excessive and unnatural sibilance I was hearing with some songs is gone. Go back to 150 hours with the Onyx, and the excessive sibilance was noticeable. Not now.
Music that had sounded excessively/unnaturally sibilant to the point of harshness, but now don't have that problem with my Onyx DAC fully broken in: Gillian Welch's Boots No. 2 Vol. 1 & 2 albums, Carmen Villain's Planetarium (Alternate Mix), Cassandra Jenkin's Telephone Ghost, many of Masha Vadat's songs, Simon & Garfunkel's Wednesday at 3 a.m. album., and the worst offender of all, Neil Young's Round & Round song.
Wow. This is really impressive. Simon & Garfunkel's Wednesday at 3 a.m. album and Neil Young's Round & Round song have generated complaints online because of their excessive sibilance, but Metrum's Onyx DAC has completely eliminated it with my system. Happy days!
I highly recommend this DAC.