I am finding inconsistencies between the DP4 mixing board and the GPO individual instrument volume settings.
Sometimes, the mixing board is totally inoperative(that is, the sliders have no effect even though volume variations are being displayed), but I can set volume in the GPO window. Sometimes the mixing board is operative but works independently of the GPO vol control. other times, the two are coordinated so that if I change one the other changes with it.
Another thing, sometimes if I set vol in GPO, when I resume playing it reverts back to where it was.
I have not done a systematic "analysis" hoping someone has a simple answer.
DP4 MIDI volume control and automation can be a little confusing at first. For starters, If you want to use the mixing board and automation to make sure you have the "use standard MIDI volume and pan CC#7/10" option enabled in GPO. Now, ignore the volume knob on the GPO interface...use the DP mixer's fader. DP send the current position of fader when you hit play, so any changes made to the GPO volume knob will be overridden. I like using the the mixer automation to balance instruments without affecting the dynamics recorded with the Mod Wheel (CC#1).
There is one drawback to using MIDI CC# 7/10 in DP, that is that the mixer's pan knob will override the panning stored with each instrument. I have gotten in the habit of making a note of the pan position of each GPO instrument as I load it, then set the pan knob on the mixer to match.
Notice that GPO has up to 12dB of gain, so you don't want to run your DP faders at 127 or you will have major problems with distorted audio. A DP fader value of 80 is roughly 0dB on the GPO output volume. There is also a minor bug in GPO where the volume knob moves in response to MIDI CC#7, but the numerical value does not change.
If you want to record automation for your Volume or Panning, use the controls just above Pan knob in the mixer...