ProtegeManiac
Headphoneus Supremus
They sound just great, my laptop volume was set to 80% and for the Icon Dac around 11-12 o-clock knob position.
more than 12 o-clock the volume is already too much, i think the Icon Dac has enough power for the HD 600.
Why not set the laptop to 100% then use the Icon DAC's volume control as a master control? You'd use it at lower than 11:00, which can mean less distortion - whether there's audible at that point already anyway means you might not really notice it, but then that's still the proper setting anyway. The only reason to want the amp's volume control higher (aside from more dB's) is if the potentiometer is so badly designed that even at 10:00 it has audible channel imbalance.