What volume level should a DAC be set to when feeding your Pre Amp

G'day All

I have an Accuphase DAC (DC-901) with a digital volume control that feeds my Pre Amp/Accuphase integrated Amp.  The DAC is fed via USB. It reports its volume level in db and altering the volume on the DAC impacts the volume level coming out of my Integrated.  I currently have the DAC set at 0.0db. This DAC level is purely a guess on my part not really understanding the technicalities of it all.  I'd like to understand better the implications of this DAC volume setting on my overall listening experience and whether or not the setting I have in place currently is correct.

Any advice appreciated.

I remember a Paul McGowen (PS Audio) YouTube video where he says (paraphrasing Paul) "Adjust the output of your DAC/CD player so you preamp volume control is in the 12:00 - 3:00 position". He said "In the old days, digital volume controls had problems sending an accurate signal but now, that has been worked out and it's O.K. to adjust the DAC volume.". I tried to find the video but could not. The bottom line is your preamp's volume control sounds best in the 12-3 range. I've been doing this recently and find that it does sound somewhat better. 
Thanks @dweller, much appreciated.