Are you using the Ifi as a volume control (preamp) also. Can you connect to with toslink. I looked it up and didn't say it could.
It's pretty mediocre as a preamp. Use is at a DAC only for best sound.
Toslink can be used but there's a limitation. You can use Toslink OR you can use SPDIF but not both. Because for some stupid reason they decided to make the Toslink and the SPDIF use the same input plug. Crazy.
It was a problem for me in my downstairs system (my HT) because I have a BluRay player that uses SPDIF and a Roku device that uses Toslink. I figured out a workaround. I had the SPDIF cable built with a standard RCA connector on one end and a locking BNC connector on the other. Now I plug in my Roku device using the Toslink and my BluRay player into the BNC input on the iDSD Pro.