No volume on DSD files

Roon is running on my Mac Mini. I use the remote library on my Mac Pro. I’m using the volume option on this remote use, in order to use my NuPrime uDSD DAC that has no volume control. Every thing is going fine until I play a DSD file/music then only 100% volume works. Whats wrong that the a 50% volume setting will not work with a DSD file/music?

This is clearly specified in their instruction manual. Roon plays dsd only at 100.