This has become a topic of great interest to me. I record the USB output of my Digitone onto my computer. I am shooting for a nominal sound-pressure-level for the resulting audio files. I find the results ca vary from one project to another. I suppose this is because there is a distinction between SPL and humans’ perception of loudness. I know there are other tools available to change the SPL, to normalize, amplify, clip, whatever, my tracks…but I am trying to avoid them. Partly because, it seems, the Digitone has all the tools I need (level monitoring would be nice; can we please see that in an update?).
Though I don’t have experience with other boxes, I think I understand what some people mean when they say the DN has massive headroom. The music I make is on the tame-side for the DN (accompaniment tracks for students to play along), and I wonder if that is why I frequently end up with an SPL a little on the low side.
Edit: You mentioned Main Volume as an element of gain staging. All I have ever done, output-wise, is record out from USB, and in this mode: Main volume has no effect on output USB sound level.
Velocity and Unison mode are part of the audio engine and increase or decrease volume from -127 to max 0. Overdrive adds gain from 0 to max 127… The master boost adds gain from 0 to 127 and master volume attenuates the total output volume from 0 at max to total attenuation at minimum.
The mixer is used to balance individual tracks between the total available headroom.
My point here is that to make advantage of gain staging it’s sometimes helpful what difference between gain and volume is. Not easy to explain and others could do probably better. Worth a google search to get more insight what is affecting a signal why and how to use it.