Reactcore
Headphoneus Supremus
@AussieMickWhich is the best setting depends upon the amp being used.
I noticed the same when playing with my Questyle HP amp between Dave and HP.
If i use Dave in DAC mode (volume -3dB) my amp sounds harscher.. it seems the more its analog potmeter attenuates, the more distortion it gives. But setting my amp volume to max makes it too sensitive to its line interlink cable received noise.
So like you, i found a sweet spot near the middle.