This one has been with me for a while....
I had a client contact me saying that he was trying to interface his Roland multi-track to his computer via S/PDIF. He had gone to a local music store, and they sold him a cable, but he couldn't get the Roland to communicate with his computer.
"Bring it down and I'll try to help", I say.
So he shows up with his Roland, and an analog RCA type patch cord. I told him to return the cable to the store from which he had purchased it, and passed on this info:
S/PDIF is a digital format that is impedance specific. You may know a guy who knows a guy that uses his stereos' patch cords, and it may even work....but only over very short distances, and error rates are going to be high.
Conveniently, the impedance selected for S/DIF was 75 Ohms, which means that if you have some spare TV or satelite - type coax cable laying around, and have basic soldering skills, you can make your own S/PDIF cables.
Basic TV coax is "RG59", and is about $0.25/ft (yeah, I still use feet....sue me.)
A good but inexpensive RCA connector is Neutriks' part number "NYS352", at about $1.29ea.
Cut your cable to length, solder a connector to each end, and you're done.
Easy....