S/PDIF-how different than an IC?


I posted this on "Cables" too. One has a 75 Ohm spec and one does not. One comes in pairs and one comes as a single. Both typically have RCA's though some have BNC's. How does a cable producer change the spec on what outwardly appears to be an identical cable? If you specify from a cable producer that you want an S/PDIF how do you know they are not simply selling you one half of a pair of off-the-shelf IC's? And last but not least, how does 75 Ohm change the sound one would hear from a normal IC (when carrying digital signal rather than analogue of course)?
I know this much; a very well-respected engineer with a Ph.D. in EE who designs and produces DAC's of his own says that you are free to experiment with using a normal IC with his DAC's rather than a dedicated S/PDIF.
128x128fsonicsmith

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Thank you Kijanki! 
Zardozz-are you sure? What you state does not match the limited understanding I have. 
Thanks all. The DAC in question (see my OP) is the SW1X III Balanced. I started out with a dedicated S/PDIF that came with BNC's but also came with BNC-RCA adaptors. My Aurender W20 offers both BNC and RCA outs among others. So I used the BNC out from the Aurender. I had to use the adaptor for the DAC since it only has an RCA input. I choose not to ID the cable maker but the cable is highly regarded though modestly priced (under $400) but in this particular application sounded dull and lifeless. 
Then, out of frustration, I pulled a 2M Analysis Plus Silver Apex RCA IC from somewhere else in my system to try. You would never believe that a simple cable swap could make so much difference. It was like the sun came out on a crappy day. Every audio descriptor or so-called attribute came out from hiding and I have been smiling ear to ear for 48 hours since the swap. Now I have ordered a custom made 1.5M S/PDIF using the Silver Apex conductor and construction from Analysis Plus. When I inquired of AP, I was told the IC would approximate but not duplicate the performance of the S/PDIF version and that it would NOT simply be a single run of Silver Apex IC. It cost me just under $800 for the single cable. 
If anyone here is interested, I will report back. Auxinput's input (pun) has me thinking I should have ordered 2M. Oh well.