How crucial is the quality of a digital cable?

I've never used RCA interconnects to transfer digital signals to a DAC. But theoretically, cables which are most resistant to RFI/EMI would least likely to interrupt any digital signal stream. My first choice is to use optical cable because it's completely immune from RFI/EMI. In my experience, the results are error-free streaming from my Apple TV at it's highest spec digital steaming capabilityy, (IRC 24 bit 48 MHz and my Sony UDP 1000ES disc player at it's highest spec into the internal DAC on my Anbthe STR pre-amp. And so far, I've heard no difference in SQ from more expensive streaming system. I'm 71 years old/; but my most recent hearing test about four years ago reveled that I can still hear 20KHz audio signals. I consider myself extremely lucky because I spent sixteen years in ambulances running a high volume of emergency responses with loud Federal Q sirens and later, electronic sirens without wearing any ear protection.

@motown-l How crucial is the quality of a digital cable?

More crucial than I had recalled. Validated it again yesterday. Quite surprising.

After running an Analysis Plus Solo Crystal SPDIF Digital coax -or- Cardas Lightening 15 digital cable for 2 years between my streamer and dac, just for grins I swapped it out for a former 5-year old AudioQuest Cinnamon Digital coax. Like it was not even close and AQ is decent cabling.

Wow, the AP/Crystal Solo digital coax is amazingly fuller sounding, more midrange, with a more impactful sound stage. It matters more than I recalled for SPDIF/Coax. Perplexing. Would not have believed it until reverse testing it.

Yet another surprising story. I changed speakers a little over a year ago and after fiddling around with positioning,swapping tubes and cables around, the sound was still "off." It couldn't possibly be the SPDIF....could it?I tried a couple from the junk box and the third one was magic.It's an old cheap boutique brand that I won at auction here on the 'Gon years ago. You never know. It replaced a Silnote that was formerly the very best in my setup. Everything matters.

I second that the AP/Crystal Solo is a fine cable. I liked it very much when I had XLR connections.

I tried a couple of coax cables and they didn't really sound much better than my RCA outs so I tried one of the RCA cables in place of them and the sound was so much better. Maybe it has something to do with being unshielded, but I really can't say.

Then I tried Toslink and never looked back. It opened another can-o-worms but I found the right cable and have the most alive sound I've heard. One also can't forget about the two items being connected as they all perform differently. 

All the best,
Nonoise

@nonoise if you get a chance, check out that test video done by reviewer named Passion for Sound on YT. He does a form of audio signal playback test with a general USB cable and five other known brand shielded USB cables. For the preparation process in the test, he captures the deltas between each with a form of inversion process. Then, actually plays back the delta itself. You could graphically see, and hear the audible range differences, and hear the different signatures peeking through between each of the different USB cables. While I'm not explaining it very well...it was interesting to show how some cables are noisier than others and the shielded quiet cables were smoother, less detail/etch with less noise. Each cable produced different measurable and audible results you could hear.