I have no issues with the midrange presented from my GMB/A2 + BHA-1 to the HD800, or with any other portion of the music frequency spectra, for that matter.
IMO, the HD800 midrange, as driven by the GMB/A2 + BHA-1, is highly resolved and engaging.
The sound stage is unrivaled by any headphones in the world.
That's why I stopped looking for new equipment (I am in my happy place).
My starting point was hearing the Yggy + Rag1 and Yggy + WA5. Those rigs, owned by Mr. Speakers, drove the HD800 beautifully.
But, again IMO, the GMB/A2 sounds nearly as good as Yggy, even perhaps a bit more engaging, and the BHA-1 provides a very neutral and sublime driver.
The music transition points are smooth, to me.
There, I mean the mid-bass to lower mids, and the upper-mids to treble. Fast and clean.
Depending on the music and production, at times I do experience a bit of brightness at 6kHz, but I've digitally EQed it down with JRiver.
YMMV, and thanks for the discussion.
RCBinTN