S/PDIF-how different than an IC?

I make my own cables. SPDIF cables are made with high bandwidth 75 ohm coaxial wire and special RCA plugs with crimp on pins to maintain that bandwidth or BNC connectors.  AES/EBU cables are high bandwidth balance wire with standard XLR connectors. Regular interconnects technically do not have the bandwidth to support the higher frequencies required to pass on dense digital information such as 192/24. Only a single cable is required as both channels are contained in the signal.

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. 

Find a set of the old A/V composite cables and strip the yellow (video) cable from it. Works fine.
BillWojo

Now I have ordered a custom made 1.5M S/PDIF using the Silver Apex conductor and construction from Analysis Plus.

I have found that BNC cables with a BNC-to-RCA adapter actually perform better than a cable with only an RCA connector on the end.

You do not want to use an adaptor. Make a cable with a BNC on one side and an RCA on the other. RCAs used for an SPDIF cable are special. You can not use just any old RCA without killing bandwidth. You can use an SPDIF cable for an analog signal but not the other way around.