Roon supports Devialet AIR

[Hifi_swlon]

The answer might be in what you wrote yourself :

- volume control mode : use device controls

What's confusing is that under "More info" in Roon Audio Setup it reads :
"Choose 'fixed volume to diable volume controls in Roon'"
"Choose 'DSP volume' to adjust the volume in software"
"The other settings cause Roon to pass volume commands to your device. Some devices implement extremely high quality hardware based volume controls, some ignore volume controls completely, and others etc...."

I was expecting that selection "use device controls" would send hardware volume commands to the D200. This works well usually with the Wasapi Air Driver : if I select Devialet Air as the Windows audio output and adjust the volume in any application the D200 volume is hardware adjusted (the displayed volume changed on the control screen of the D200). But not with Roon. 

Bug ? Anyone being able to adjust the volume on his Devialet via Roon Control ?

This is just my opinion, but I wouldn't like to use Roon to control Devialet's volume. It would be too risky because it's way too easy to accidentally set volume to 100 % in Roon. That's what happened to me once I was listening with my headphone setup. It's wasn't a pleasant surprise to listen music all of sudden with 100 % volume. So please be careful with Roon's volume control. I hope Roon would re-design the volume control at some point.

I've been there too on my kitchen speakers. Ouch!

Would definitely not be happy with anyone being able to do that to my main hifi, and would set Roon to fixed volume if it could control the Devialet volume directly. It's also waaaay too sensitive on the iPhone.

I quite like the Devialet remote (physical and ios) anyway and would probably prefer to use them regardless, unless Roon made major changes to their control.

I feel confident they're aware of it needing improvement, or I'd hope they at least allowed a max volume to be set.