@icedquinn The big advantage of spidif is you reduce the length of the pre-amplified signal needs to travel and make it digital. So it wont pick as much RF noise
Long runs of copper make great anntenae for picking up spurious EMI. By using an extremely high frequency for the carrier (IR or visible light) it makes it very easy to shield the "conductor" of the signal with any material that is opaque to light.
That means the only source for EMI is in the electronics within the amp/source and the speaker, which is much easier to shield or otherwise mitigate than a long cable.
Yeah, I was going to mention digital, like using a USB mic instead of plugging an analog mic into the old phono jack in the PC.
If the comm protocol can detect errors then it will not pick up any noise in the signal itself. But the copper can still carry EMI to the other electronics other than by being carried by the signal.