SPDIF cable same as coaxial cable?

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. 

if you are running optical spdif the key, an absolute key, is to get a true glass fiber (not plastic) cable - with this, the sq gap is equalized to electrical spdif

there are some reasonably priced ones out there, just search

but know that alot of the ’audiophile’ toslink cables marketed out there as such are still plastic conductor...

Digital Coaxial is considered the better way to go, at least from all I’ve read. So that is what I use. However, to be honest, I’ve used toslink or photo optic cable prior and can’t say I notice an apreciable difference in sound quality. Same thing with the silver cables (silver plated) VS copper speaker cable debate.... they both sound good to me. I like my Qed silver anniversaries....however, when I can afford them, I will grab a pair of auditorium 23’s....

Does SPDIF just take the I2S format and just change into a single connection instead of 5 connections.