How can I tell if I need a better clock for my DAC?

The issue posed by the OP was about a better clock.  So my response was about clocks.

At the current state of the art, a femtoclock, while not a sufficient condition is IMO a necessary condition to the best possible SQ.

Also, generally speaking, if a maker implements a femtoclock, chances are the rest of the unit compliments it.  In other words, it's a good sign of quality . . . generally.  If Steve N. wants to provide exceptions that he knows of, I'm all ears.

Thanks, everyone, for your inputs.  Unfortunately, much of what was said went over my head.  Could someone recommend a good, readable reference on dacs?

Proper spdif connection between transport and dac should be made using 75ohm bnc.
rca is not true 75ohm and this can also introduce jitter.

https://www.markertek.com/productImage/450X450/B-PF.JPG

https://www.amphenolrf.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/0/3/...

Cheers George

Here's an article that touches om the subject even though ge talks more about usb inputs. He also has a list of components he recomends, including dacs.
https://darko.audio/2013/07/when-should-you-use-an-external-usb-spdif-converter/

I suspect a lot of new dacs sound better than your Cambridge but it doesn't have to do with just jitter.

Thanks, everyone, for your inputs. Unfortunately, much of what was said went over my head....

You’re welcome. Honestly I think you may be over thinking this. Go with whatever your monetary budget allows, your personal listening impressions, manufacturer reputation and other customer testimonials. After all that then consider jitter and other technical measurements. Just my recommendation.