SPDIF cable same as coaxial cable?

The above is a very thoughtful and informative answer.

Is a coaxial cable same as a SPDIF cable?  Seems they are one in the same.

The simple answer in home audio applications is yes.

Coax with a BNC termination will conform to the 75ohm S/PDIF standard.
I have been told by a cable designer (Rick Schultz) that RCA digital coax can come close to 75ohms depending on the design.

http://www.bluejeanscable.com/articles/75ohmrca.htm

auxinput,
great job!

AES/EBU - uses an XLR cable that should be engineered to have 110 ohm impedance.

Like with S/Pdif, AES/EBU is an audio transfer standard and not the cable.  It can be used with 110 ohm XLR cable (IEC 60958 type I), with 75ohm coax or Toslink (IEC 60958 type II).    XLR is just most common cable with AES/EBU.

The main difference between S/Pdif and AES/EBU standards is in the property rights.  S/Pdif includes Serial Copy Management System, preventing second-generation copy in some instances.  Most of AES/EBU used in consumer audio is S/Pdif standard.  It is assumed to be 110 ohm XLR only because that was the most common use of AES/EBU (studios).

Also, AES/EBU was defined as 24 bits while S/Pdif was 20 bits + 4 auxuliary bits, but these 4 bits are used (almost always) as data extension to make total of 24 bits.

So, in consumer audio both "AES/EBU" and "S/Pdif" follow S/Pdif standard and name difference is customary for different cables and electrical levels.

If the AES3 XLR cable can be connected to RCA with a simple adapter it is SPDIF which is really now considered a variant of AES3 if you need an impedance converter for it to work it is AES3 type 1 or the old AES/EBU standard. AES3  is used in professional installations with XLR 110 Ohm balanced or BNC 75 Ohm unbalanced.

I recently purchased a blue sound node for use with an external DAC. After first trying with optical cable, switching to coaxial output made a big improvement in sound. So I would definitely avoid optical cables.