I used a spare RCA interconnect (nominally 50Ω) for Spdif when I first got a DAC, it worked but a cable designed for the job but with RCAs on both ends was quite an improvement and a 75Ω cable with BNC connectors (Belden 4794R) better still even though it was designed for 12G SDI video and I had to use an adaptor at the DAC end because Rega didn’t see fit to put a BNC socket to their DAC. I think they were all coax cables.
