Confused about adapter for RCA to BNC

That CD transport has an RCA digital output for SPDIF. is it non-functional?

If you are just trying to use the BNC cable I think you would be much better off with a properly designed SPDIF cable.

That said, I found a company that sells a $2000 cable which is a BNC cable with BNC to RCA adapters.

https://www.thecableco.com/tyr-2-s-pdif-digital-cable.html?gad_source=1&gclid=CjwKCAiA2cu9BhBhEiwAft6IxA3nq_ZVJe4rKkRnPxoGwUHCnpD1UUWtFUOVqhNu1gXTwjQwXqi34xoC3_EQAvD_BwE

For digital signals I always recommend silver or silver plated conductors.

Wireworld Wires will make you a cable with BNC on one end and RCA on the other.  I bought one for a clock to DAC and it is much better than an adapter.   

Some adapters are 50 Ohm and Some are 75 Ohm so be aware if you use an adapter,  you need a 75 Ohm 

I would go with a factory made cable

https://wireworldcable.com/products/starlight-10-coaxial-digital-audio-cable?variant=47931732623656&country=US&&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&srsltid=AfmBOooTBKmwaWEZNWx1JI9tvdkcsAFhzzEJ4_cDKSOSLG__ZoD2CX6mpno

They make higher grades , this is an example. 

If you order one they are available as BNC to RCA or RCA to BNC.   If the source is RCA and the DAC is BNC you want a RCA to BNC.   It has to do with the grounding I believe. 

@stuartk confirm the specs on your bnc cable to make sure it is 75ohm before you buy adapters 

I’d rather use AES from transport to DAC or a proper 75ohm coax cable and not introduce any adapters unless you have a fancy and expensive bnc cable that you can’t part with. I wouldn’t add variables such as adapters to compromise the results.