Although the THD is still excellent I just wonder why I have so much noise ? The noise cannot comme from the ADC nor the computer because it was good on optical with the same other connections, I mean USB powered on the desktop on the SU1 and USB powered by laptop on the ADC.
AFAIK Optical SPDIF is immune to grounding noise, while USB isn't.
Do you have another USB DAC to compare against with a THD+N supposedly below -95 dB?
I see you brought the USB-C splitter cable but mind that it will only remove grounding noise coming from the power pins.
If your computer is not properly grounded or there's AC noise it will still end up in the SU-1 via the data pins.