AudioQuest DragonFly 24/96 Asynchronous USB DAC / Headphone Amp

[clar2391]

I just got my Dragonfly yesterday and I'm really enjoying it with my MacBook Pro. I'm confused as to which volume control to use in order to take advantage of the analog volume control in the Dragonfly. Do I use the system volume control or the iTunes volume control, or does it matter? The documentation is unclear to me. I know one should be set at 100% and the other should control the variable analog output.