I have some BNC to RCA adapters I used to use for my component video cables. Can these be used to connect to my RCA SPDIF cable and if so will that cause any degradation to the signal transmission?
Of course no adapter is always technically better, but I think it's less of a problem than using an RCA cable that isn't 75 ohms. While there's no shortage of 75 ohm cable, I don't think any RCA connectors are true 75 ohm.
Canare makes a "75 ohm" coaxial crimp connector that comes closer than many others, but I think it's a physics thing - the RCA coaxial dimensions just aren't big enough to maintain the 75 ohm impedance. It's really a shame that RCA became the standard for consumer video and coaxial S/PDIF, while most all professional and prosumer equipment uses BNC for both.
So I think it's likely you won't discern a difference between using the adapter with an RCA cable versus having a RCA to BNC cable.
Steve