Deleeh
Headphoneus Supremus
Use optical if possible. I2S will just return you here with connection problems. If there are differences at all, they are miniscule. And what's wrong with the Eversolo's DAC?
I looked at the Eversolo A6 Master Edition, it doesn't have I2S, but HDMI output.
Which means you could connect it to a Dolby amplifier theoretically.
In that case you can only connect to the R26 via coax or usb out (audio).
You would have to ask the Eversolo threath or room community if it would be possible to use Roon in such a way that the Eversolo can be integrated into the network as an integrated streamer.
If so, you could integrate the R26 into a zone and operate it conveniently with a smartphone, tablet, laptop or PC.
If the Roon app is installed.
Otherwise it would only be possible to connect coax or usb out audio, but I don't know if the internal dac of the Eversolo will intervene or not.