I use Roon with two devices: a Logitech Transporter and a Raspberry Pi3/DietPi. These two devices are connected to the same DAC. The Transporter is connected via AES; the Raspberry via USB.
In Roon I have set up both audio devices as follows:
Transporter - with Disabled Volume
USB Audio DAC - with Fixed Volume
When I play the same track the sound coming via the Raspberry is always louder than that of the Transporter. Is that normal or is there a something else that I need to adjust in Roon?
Try volume leveling.
It can be accessed in the “Zone Settings”. You might want to group your zones before to compare the effects.
Thanks!
I tried to group the the device but learned that the Transporter (Squeezebox Zone) and the Raspberry/Dietpi (RAAT Zone) are of different type and cannot be put in the same group.
Under Zone Setting I adjusted ‘Volume Leveling’ to Auto. But that did not fix the issue.
Back to square one… 
Different DACs has different volume output, and I don’t think Roon compensates for that. So Roon sends a volume leveled digital stream to a DAC, but has no control of what happens inside the DAC.
Thank you Magnus. I just learned that the USB input in the Bryston is actually fairly old and limited (not asynchronous; playback limited to native 44.1khz and 48khz; 16 bits max).
So even though I am using the same DAC, the problem is most likely a DAC input issue.
Thank you very much!