If you have internal gain switching in the DAC depending on the dial position or not this will make the difference
In the first measurement I just used E-MU's (crappy) headphone's output pot.
In the second,pot is full on and just dialed down analyzers input level.Have a look at the difference in THD,almost 15db!
(see the second one I changed,it has a glitch before)
(No volume control on that chip,it's 15 yo AKM4396)
Edit:When I find time I'll do the same for Khadas who has VC like the new DACs,stay tuned.