Thanks for your patience here while we’ve looked into this!
We contacted the team at Hegel regarding the capabilities of the H80. The team has confirmed that the device does not support USB HID volume controls.
If you’re unable to adjust the volume using the knob on the device, and power cycling doesn’t change this, they’ve recommended taking the device in to your local Hegel dealer for assistance.
If the problem is just that you can’t control the H80 volume on your new computer, then this is as expected. Some OS’s just pretends that the connected device support HID volume control while actually adjusting the signal level in output PCM data. So driver setup or version differences on the two computers could make it seem like the old computer adjusted the volume of the H80 (this would not update the amp display).
I’m glad to know that you were able to find a solution! As mentioned above, you can always try Software or DSP volume options to control the device from Roon as well.