Perhaps it's literally as simple as the ribbon drivers in the speakers and the cables and everything else have continued to break in and settle down. I am just not hearing the upper midrange brightness anymore.
We listened to the entirety of Dido's No Angel album last night. I heard no upper midrange brightness, and, as you know, I am focused on this upper midrange brightness issue.
David Blumenstein has been staying with me since Friday. He now has by far the most ear time on the system of any visitor.
I do not want to speak for David, but he has indicated to me that he has not heard any upper midrange brightness problem.
David brought over today Grover Neville, whom I had the pleasure of meeting for the first time. Grover studied at the Oberlin Conservatory of Music. He is a recording engineer, a musician and an artist, as well as a high-end audio reviewer. He's much younger than we are, and he likely has most, if not all, of his hearing range intact.
I inflicted upon Grover my usual speech that "only criticism of the sound of the system is helpful; praise is not." Grover was with us for only an hour or so, but he did not report any upper midrange brightness. Grover actually commented that the tonal balance of the system is, if anything, a little bit "warm" for his taste.