Hi Joachim,
Are your sure that a USB cable without power will work between the PC and the NOS1(a) ?
2 years ago I had an Sotm USB 3 PCIe card that has a switch to allow sending the 5V power in the USB cable or not.
To establish the connection it was necessary first to allow the power to flow between the PC and the NOS1, then (and only then) as soon as the 2 components connected, I could switch OFF the USB power...
I would test with an ordinary USB cable (on which the power is "masked" with a thin layer of isolation tape or plastic) first just to be on the safe side...
It seems that some dacs do not require this, but the NOS1 seem to use it at least for the connection time... (Peter ?)
Alain