SPDIF / OPTICAL IN PLAYBACK LINUX

Never tried spdif, but I would guess that the Zorin instructions cover different devices or a pass-through situation.

Although I similarly guess you could make a transparent light emitter it is an unlikely device, so two way on one spdif connector is also unlikely.

Normally you select the connectors in sound setup. Certainly that is where the spdif option appears on Windows. Ubuntu Linux is a bit Carp for sound and does not seem to have any options.  You could try this link.

As far as I know spdif is one way, so the signal is digital on the way out and then needs to be converted to analogue at the end of the chain.

I use spdif out via optical cable.

Below is some info on PC audio streams that it took me ages to decipher.

The intel HD audio hardware is contained in the PCH or newer ICH chips. The hardware consists of 4 or more DMA engines that can be configured for input or output and they read or write to a memory buffer that an App or the OS has to manage. Data to/from the DMA engines is connected to the Intel designed HD audio bus. The HD audio bus is designed to have audio end points (usually codec’s) connected to it, each with its own ID. I have never seen a motherboard that exposes the HD audio  bus to the outside world so the only device ever connected is the onboard codec.

The Windows core audio subsystem has another way of generating audio streams which uses the CPU to read a buffer and then write the data out to any bus on the system, that’s how sound data gets delivered to USB and PCIe devices.