I have no real experience with Roon volume because my streamer is fixed volume and volume is controlled by the preamp.
However, if I understand correctly, yours is a timely question because this seems to be addressed by the new version released today:
This is the new version 2.0, Build 1167. However, you need a little patience because this update is currently on hold, due to a startup problem that was discovered with this version for some users. There is currently a banner at the top of the forum with this information, and a few threads. A fix is expected soon.