With fixed volume in roon it is not possible to play dsf files

It is not possible to play dsf files with fixed volume.But only with dsd volume. But this means a lost in sound quality for me.With fixed volume I can use my exit of my lampizator dac. Now I want to know is it possible to use the fixed volume with dsf files ? And what have I to change in Roon. I use DoP.Thank you