Tor the Roon Ready device is the EX and the Audio Device is your C2600, if you open the cog on EX Roon Ready you will see the C2600, also, the C2600 is a Roon Tested Dac and info can be seen in the Signal Path, it is not a Roon Ready device as such wont show up as a Roon Ready device.
Volume is controlled via the Roon app.