Given that these are studio monitors using the volume control on them is extremely inconvenient & unnessesary not to mention would not even be tolerated in a production environment as the volume controls are seperate & difficult to get perfectly balanced. they need to be perfectly balanced at thier max intended volume & left there. Use you computer volume control to adjust volume making sure that the sample bit depth is set to 24 bit in you operating system.
Max intended volume does not mean max volume but the max volume you intend to use & that is within the power capability of the monitors amps. This maximizes the range of available volumes available from your computer.
You should not hear any degradation with it setup this way. There is too much misinformation on this subject curculating on these forums. The easiest way here is in fact the best way. Bit perfect ASIO drivers that remove any volume control from the computer are unnessessary, Just use WASAPI. Does essentially the same thing but doesn't rob you of volume control. Sound quality is the same. WASAPI though will only support those sample rates that are supported by your sound device so some files may not play if unsuported by your hardware configuration which is funny because the suposed bit perfect ASIO drivers for my souncard will play them but WASAPI won't.
Looking at your USB DAC I'm not sure of the quaily of the volume control in it though you could use it instead of the windows volume control if it tracks well channel to channel, This is the bane of most cheap analog volume pots is they don't track well. If the volume tracks well & you hear no shift in the image when adjesting the volume pot then you are good to go. If you do hear a shift in the audio image then use the windows volume control asd this will maintain perfect channel balance.
Found a review that indicated very good tracking of volume control pot on your USB DAC so I would go ahead & use that.
Edited by germanium - 12/11/11 at 11:31pm