Native DSD is supported.
I haven't tried the volume, I have it fixed. I use the volume on my amp, which has a remote control. I will test it out later and will update this post with the feedback.
UPDATE:
I tested the device volume: If I set it to device volume it doesn't allow Roon to change it. It still says volume is fixed. So I assume the Linux driver doesn't support changing device volume (same as with MAC OS).
I did try it out with the DSP Volume and it will work, but MQA files will not be detected if Volume is in any position apart from 0dB, which I expected since you are modifying the original stream. I tested it with a MQA.352.8KHz file, and as soon as I move the Volume from 0dB, it goes to PCB 44.1KHz.
If you are not into MQA that could be the option, using DPS Volume from Roon.