FWIW I did post my question to the "Ask the Experts" forum at PS Audio. A couple of experts (Ted Smith, designer of the Directstream DAC ,and Galen Gareis, longtime Belden cable engineer and designer of Iconoclast Cables) have weighed in. I've learned a lot about balanced wiring variations. No one has yet had an answer to the question about how the BHK preamp is wired.
https://forum.psaudio.com/t/how-balanced-is-the-bhk-preamp/11556
https://forum.psaudio.com/t/how-balanced-is-the-bhk-preamp/11556