Bluesound Node - USB Output is only Fixed Volume with Holo Audio Cyan-2

To everyone who can help,

I connected my new Holo Audio CYAN2 DAC to the Node(N130) via USB output and I have the problem that the volume is only fixed, but I would like to change volume with Roon, Spotify or Tidal.

As far as I understand it, volume control (using Roon/Spotify/Tidal) is possible via USB. Note that I can use volume control using the optical Toslink and Coax interface, but the sound quality is less in my case. Therefore, I prefer to use USB.

Can you confirm that volume control is possible with an external DAC using USB?

It looks like the CYAN2 is properly identified by the Node as "Holo Audio UAC2.0 Gen2.1". I can see this in the Audio settings in BluOS. However, in Roon the option 'DSP volume' for Volume Control in device settings is not available and the 'Device volume' option does not work.

I have tested the CYAN2 with USB directly to the Roon Server (on Linux) and volume control works fine with 'DSP Volume' option (the 'DSP volume' option for Volume Control in device settings is now available). However, 'Device Volume' does not work.

On a side note, I had the opportunity to test with a DDC (Denafrips IRIS and GAIA) between the Node and the CYAN2 (using USB). Same issue, only fixed volume! However, If I connect the Denafrips DDCs directly to the Roon server I can change te volume using 'DSP volume'.

To me, it looks like a USB protocol related issue. 

I hope someone can help.

Thanks, Alexander