Ok, I partly confirm. Did the following:
1. Powered up the device with the headphones plugged, Volume seems normal
2. Unplugged and replugged the headphones, volume is low
3. Turned Headphone volume all the way down to -33 and back up to 0, volume seems ok
4. Unplugged and replugged the headphones and volume is much higher, though from what I can tell about my DT-770 Pro, that level is comfortable
@jesseverhage Can you confirm, that the two output plugs are stable in regards of volume? I wouldn't like any (especially loud) surprises when running the MOD in front of my amp.