NO sound from usb Imac to usb Hegel amp [Resolved]

Hi guys. I connected my Imac with usb to my Hegel amp (usb). I can see in the display of the amp that he know that the file is 44.1 or 96Khz but I get no sound. IN SYSTEM PREFERENCES of the mac i selected the usb of my amp and the volume control in roon is Fixed. I also connected my oppo to roon . He get’s the signal from my network and from his digital out he is connected to the coax in on my amp and that works. But I want usb to usb. What am I doing wrong?

I’m flagging @support, but it would also be helpful if you could post screen shots of all the playback settings for the Hegel.

First problem is solved. the length of the USB was to long (10 meters). I know make connection with my Oppo 4K player in my network. The player is connected with his digital out to my Amp and now I do have sound. BUT how do i get the best possible sound out of this combination. What are the best settings for volume etc in the set up of the Roon settings?