Confused about adapter for RCA to BNC

@stuartk - I have the same DAC as you and used a BNC cable (Oyaide 510 ) with adaptors without any problems.  Later, I needed a longer cable and purchased another of the same cable except the longer cable had rca connectors.  I compared the cable with adaptors vs. the longer cable without adaptors and I heard no difference between the two.  Even compared to AES/EBU, I did not hear any reliably consistent differences.  USB may be just a tiny bit better sounding, IMO, but the perceived difference may also be personal preference.  
You found and linked a fancy-schmancy Cardas adaptor.  Just make sure you get the female bnc to male rca version.  In contrast, I used the type of adaptor kr4 was referring to and exactly what was linked by @knownothing for the comparison I described above, and it worked and sounded just fine for under $2, which is what  it should cost to resolve your issue. 

@stuartk - I agree with @marco1 on both the adaptor and "your Craftman style home and listening area."

Back in September in my 6 DAC thread, you commented on our styles being similar.  I do have a few pieces, some old some not so old, but your place is the real deal and the vibe is very cool.  Congrats on maintaining it as the builder intended!  BTW, is that a red husky laying by the doorway?  I have had 6 of them!

@retiredaudioguy - Damn huskies, ya never know what they are up to 

@stuartk - The analog rca jacks in the X SE are "Furutech rhodium plated low-mass RCAs directly soldered to the PC board." The digital S/PDIF rca jack looks different so I am not sure whether that is a Furutech or not. However, I have never had an adaptor or digital rca cable fit loosely so that is very odd about the Cardas adaptor.

@stuartk - I am glad you got it to work.  Enjoy the DAC.

I am surprised more equipment manufacturers do not use BNC connectors for digital cables.  To me, they seem to make a better connection than RCA.