Mmmmm you may want to read http://www.epanorama.net/documents/audio/spdif.html
For those interested in the data structure used for S/PDIF, it can transmite either audio sample (PCM) or data bits (DD / DTS) in an encapsulated 32-bit word (subframe) - as follows:
0-3 Preamble (see above; special structure)
(A 24-bit sample can be used (using bits 4-27).
A CD-player uses only 16 bits, so only bits
13 (LSB) to 27 (MSB) are used. Bits 4-12 are
set to 0).
(When this bit is set, the sample should not
be used by the receiver. A CD-player uses
the 'error-flag' to set this bit).
31 Parity (bit 0-3 are not included
Seriously though, the real question is where you want to decode the data, and what devices you have that can do the required tasks – the transport layer is almost irrelevant. Both Ethernet and S/PDIF have the bandwidth required to transport DATA STREAMS required between devices - it is much more important to understnad what device in the chain has the CODEC required to convert it to an Analogue signal.
Typically a main steam Receiver (to date) handles the decoding and amplification of PCM, DD, DTS, and MPEG-Audio data streams transmitted over S/PDIF.
Support is now appearing in these moderate priced Receivers that can decode additional formats (eg MP3/WMA/SACD/DVD-A) as well as accept additional transport layers which these formats can be transmitted over (eg Digital Radio, Ethernet both in wired and unwired formats,USB etc).