Volume Settings/Control - DAC vs Preamp?

I have a Bluesound Node 2 as my DAC and the Bluesound App has volume control. This is connected to my tube preamp which obviously has a volume control as well. What is the school of thought on volume settings and where to control volume during playback? Should I set the DAC's volume to a certain fixed level (and what should that setting be - low, mid, all the way up?) and adjust volume from my preamp? Or vice-versa? Does it matter? It's way easier to control volume via the Bluesound app as my preamp has no remote but I can live with either solution if it makes a difference.

I have combed through a number of similar posts but not sure I got a clear answer.