Proper spdif connection between transport and dac should be made using 75ohm bnc.
rca is not true 75ohm and this can also introduce jitter.
https://www.markertek.com/productImage/450X450/B-PF.JPG
https://www.amphenolrf.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/0/3/...
Cheers George