Typically you would probably have MULTIPLE devices along the chain which would have a volume control present. So you just need to experiment with EACH one, to decide where to put it so that you're (a) happy with the final result, and (b) satisfied to use one or more to adjust levels whenever you need to.
For example, my source devices (BluRay player, DVR, etc.) do NOT have their own volume control. But they all go through my Yamaha AVR, which DOES have a volume control that I like to think of as my "system volume control". So I set that at 0, which allows me to make +/- adjustments intuitively. This is the one and only "system volume" adjustment I use, with my other downstream volume controls adjusted accordingly so that the AVR volume control is all I ever play with if necessary.
The 8 analog preamp outputs from the AVR go to the [non-HDMI] Realiser. I felt the -19 default factory level on the Realiser was unacceptably low, and I increased that to -10. I never further adjust the Realiser's volume, with -10 built into each of my presets.
The optical output from the Realiser goes to my Audio-GD NFB9 external DAC, where I've set its volume control almost to "maximum" (i.e. 46 out of 47). Never adjust it further.
The XLR output from the DAC goes to the XLR inputs of my Stax SRM-007tII/SR-009. I have the amp's volume control set at 2 o'clock, and I never adjust it further. In fact, that's how I came to set the DAC's volume control to 46, because with each of the other upstream volume controls where I described them, and the Stax amp's volume control at 2 o'clock, I was satisfied for average source content when the DAC was at 46.
So I now only use the AVR to adjust "master volume", with typical content requiring volume from 0-7 to satisfy me.
And in that system, the Realiser has been set at -10, which seems to work great for me.