[stino]

Along the lines of there is no such thing as a stupid question, here goes nothing.
I’m using an external USB DAC. What’s the best volume setting to us in the OS (Windows 7 in my case) to drive the DAC. Will a 100% oversteer de OPAMP in my DAC or will to low an output setting lack the power to drive my amp.  There must be an optimum here somewhere.
Ideally I would like to control volume through the OS software, but there must be a catch here, otherwise why would most DAC’s with integrated pre-amps have separate volume dials?
Thanks,

 

[GloryUprising]

It's generally recommended to max out the digital volume in your OS and use the analog volume (EG the one on your amp) control when possible. 
 
If there is no volume control in the analog domain, it's recommended to control volume at the last possible part in your chain (generally again at the amp).
 
 
In the end YMMV.