It is now working.What happens? There will be some error in the CamillaDSP logs, what does it say?
Yesterday I connected up the RCA jacks to the SPDIF on board headers of the MCHStreamer kit, and I flashed it with the SPDIF_Only firmware. Then I changed from from using TosLink to using RCA cables.
Changing from TosLink to RCA should not have made a difference, though. Perhaps cold booting the Raspberry Pi and/or the MCHStreamer was needed, it is hard to tell. I don't see any issues in the log file.