I seem to remember reading somewhere that the data handling chipset that one of the Naim players uses (it might be the CD5) is a very standard one, and that it was, in principle, capable of SPDIF output. However, to do this it needs to be initialised differently, so you would need to replace the stock firmware with custom firmware, as well as wiring the appropriate output pin to a buffer and transformer.
Sorry, I can't remember where I saw this, nor exactly which player it applied to.