It appears you can’t use negative numbers for the max and comfort volume limits.
Trying to set via an iPad, the negative input numbers are made positive.
The ‘zero’ seems to work, set by default at -97.
Just FYI. I’m sticking with my digiOne anyway for the time being. (I did get rapid stutters/popping in my 5 min AIR experiment, having not had a single glitch through the digiOne throughout months of listening. Bought back some deep and painful memories)
Seems to work for me, using Roon 1.5 on a Mac: I have the Comfort limit set at -10 dB and successfully just set Max to -5 dB. (Mind you, I didn’t try upping the volume to see what happened at the limits.)