220 Pro Volume number shown in Red color and muted

[audio_engr]

It’s Digital in. And it seems turns red when there is a strong bass in the sound.

Try Analog RCA IN. See if this gives your Devialet the same symptoms. I think it won't. 

Then, setup the digital volume of your N31 to 0 dBFS and connect using AES/EBU. If this still gives the same symptoms, try USB.