As far as I understand DPS only saves the volume when it’s exited while the currently active soundcard is not DPS. In this case the DPS volume is set to the highest value of either the current DPS volume or the currently active soundcard volume but at most 75%.
So you could e.g. do this:
- Set DPS volume to 50% or lower. Quit the DPS software completely. (Do not just press the B button, actually exit DPS!)
- Set the volume of your actual soundcard to 50%. Dot not switch to any other volume control. Your actual soundcard needs to stay the currently active one!
- Reboot. Both DPS and your actual soundcard should now be set to 50% volume.
At least that’s how it works for me.