The most important thing here is that typically and I personally don't know about the Directstream Dac but most dacs do it, you set the Dac at full volume, you will most likely bypass any DSP stage, DSD to Pcm internal conversions, and possibly even filters leaving the source mostly untouched, if your preamp is good I think that would be the best way to go
Control volume with DAC or Preamp?
My DAC (PS Audio Directstream) has a volume control and so does my preamp(Benchmark), of course. What’s the best way to control the volume of my system to get optimum sound...turn the dac to maximum volume and use the preamp to make adjustments , turn the preamp to maximum and use the DAC for adjustments, turn each of them up part way? Or does it not make a difference?