A week ago I asked Gustard about the 'pin 15 dilemma' and they suggested I apply 3.3 or 5 VDC to that pin and connect the ground to pin 19. Today I finally made a test cable and it works! It sounds sublime with
Topping M50 > USB > Audio-GD DI20HE > I2S concoction below > A26
when 5 VDC is applied to the yellow-brown breakout cable.
So now I will make a cable proper with twisted strands, shielding and a 5 to 3.3 VDC LT3045 converter that I still happen to have. The lower the voltage the better I presume and the LT3045 also cleans things up.
I am a happy camper!
Any suggestions for finalizing the cable, such as type of shielding, would be welcome.