You used Gustard U12 with Audio-gd DAC? Pardon me, which model of Audio-gd DAC do you own?
As far I know after implementing USB-32 especially with recent models there is no scope of noise to pass through from PC to DAC as the +5V has already been disconnected (read the highlighted line at the beginning in orange color:
?????), instead it has own power supply. The best you can do is just cut the red wire (+5V) of USB wire or just use a cello tape to cover the +5V pin and then it will be a instant upgrade, black-silent background immediately felt (I did it myself).
So if u have Audio-gd DAC with USB-32 there is little need of device like Gustard U12.