This is just bad advice really. I come from the same purist view of ”don’t touch the digital signal” but after measuring my system and fixing the one bad and boomy room mode with Roon DSP, I’ve changed my mind. I also upsample with Roon DSP which gives a small but noticeable improvement.
Lastly about Roon volume control, you might want to check this thread and white paper:
I actually use Roon DSP headroom of -12dB to be able to use less digital attenuation on my Linn streamer. I compared these and Roon volume control works better than Linn when you listen to very low volume levels like -40-50dB.