make sure you are using an actual SPDIF cable not a RCA cable, you can buy one on amazon... i use Apogee SPDIF cables, no problems, and clarity is amazing!
https://www.amazon.com/Geistnotes-Apo…R/dp/B01N29180M
Apogee make the top digital converters in the world. thus their cables are reliable.
hope this helps.