At last, I am closing in on this project as depicted in my new system photos.
I have just rewired the Behringer as discussed above with Elizabeth: still HDTV / Cablebox and PC into a Digital Optical splitter.
Therefore Digital Optical out into the DEQ2496, and in turn, DEQ2496 out into the Zodiac DAC - using optical cables all around.
The good news is
1) The signal path seems to be working, sounds fine and I can switch between sources successfully
2) Although I NEVER remember how to do it, I somehow had the pink noise, microphone and RTA working this morning - at least to the extent I could see the EQ curve adjusting itself and hear corresponding tonal changes in the pink noise.
The bad news however, is when I turned off the pink noise, I can still see the adjusted curve when I press GEQ, but can't hear the EQ in the signal path with the music.
My usual EQ / curve test: when I toggle the Behringer BYPASS button on and off there seems to be no change (?)
My hearing is not what is was as a kid, but pretty sure it's not yet that bad if anyone who has mastered this complicated beast can comment or help.
Thank you.