So it's possible if the player is either a Blu-ray player or media streamer that doesn't have a setting to select the desired output channels that it still may down mix by reading the EDID signal that the HD621 is broadcasting?

Living Room Kit: 861v4+ID40, DSP7000, DSP5500, DSP5500HC, HD621
Bedroom Kit: F80
QNAP TVS-471, Roon, iPad Air2