Using endpoint volume control instead of amp volume control

I guess this is a pretty simple question, but y’all will never get to meet me in person to heckle me so here goes.

I have a Cocktail Audio X45Pro Server/Streamer/DAC, which feeds a Vinnie Rossi preamp/amp. The connects are balanced XLR.

When I select “fixed volume” under the Cocktail Audio settings, of course it’s fixed. But even when I select “device volume” and adjust the volume knob, there is no change in volume. Of course, when I adjust the volume on the preamp/amp, the volume changes.

Basically trying to see if I can use RooDial to remotely control the volume on my system.

Thanks in advance!