I spoke with Alvin at Denefrips about this a few years ago and he said it will work.
I never bought the DDC from Denefrips.
I use ROON RATT as my protocol so my volume options maybe different. I would look at setting the volume as FIXED on the Sonic Orbiter OS. You can them control it from your IRIS (if ROON) or set the Iris to FIXED and use a preamp.