Homeplug spdif

If by "Homeplug" you mean the over-the-powerline local area networking system... I believe the answer is "maybe".

As I understand it, this form of LAN is packet-oriented... basically it's like a lower-speed Ethernet, with a different PHY (physical- access) radio layer. It wouldn't have any ability to understand S/PDIF data frames, as they aren't packets with any sort of structure it could handle.

You could have a device (i.e. a computer) which receives an S/PDIF signal (e.g. through a sound card), turns it back into digital audio data, wraps it in a TCP/IP stream of some sort, and sends it over a HomePlug network connection to another PC... which would reverse all of these steps, and generate a new S/PDIF signal (or plays the audio). Buffering and synchronzation would be really tricky, due to different clock rates on the PCs, jitter, network congestion, packet loss and retransmission, etc.

Without a pair of PCs (or the equivalent), though, the answer is probably "No".

No.