Hi R, thanks for the questions.
First, DSD cannot be mixed or volume adjusted. It is what it is. So when we record the input microphone preamplifiers are used to set the gain.
Once recorded we have two choices for mixing: DXD or analog. In the past, we have gone analog but that has a number of disadvantages (minor). In our modern methods we chose DXD. Converting to DXD in the way we do it (on Pyramid or Zephiir) is almost (if not completely) indistinguishable from the original. I can’t hear any difference.
When we’re ready to master, we leave DXD as the master. In fact, as of yesterday, you can now purchase Octave masters at 352.8kHz (DXD). We then convert back to DSD by going analog and then back to DSD at 4X and 1X.