Don't know, with hindsight, if uninstalling the existing card was totally necessary, but there seemed to be something within the installed Realtec software that was causing me trouble and I couldn't find a way around it.
The Fireface and totalmix seem to be the cause of the confusion. The fireface, unlike other interfaces I've used that were much more basic, has 3 levels - inputs, playbacks and outputs. And unlike those previous devices, when I used to set up the audio options in the control panel, I would select the output that my monitors were on thus routing sound to that output. However, in the fireface, we appear to be routing audio to the designated playback channel rather than the outputs. From there, we route the playback channel to the relevant output.
My final conclusion is that routing the control panel settings to the analogue playback channels doesn't work as they rely on ASIO enabled sotware to playback audio, which is why sequencers like Cubase work pefectly well routed there but WMP doesn't. However, routing the control panel to SPDIF playback channels doesn't automatically send the audio directly to the SPDIF output on the fireface, but to the relevant playback channels inside the fireface. WMP and all other audio sources seem to have no problem routing their audio there by default, then its a simple matter of routing the SPDIF playback channels to whichever output on the fireface where your monitors are located, in my case Analogue1+2.
I'm coming to the conclusion that this is by design and just isn't explained well in the RME documentation. As I said before, I reckon its only good fortune on my part that my previous setup was configured to SPDIF output as a result of being sold an SPDIF cable with my monitors and me being determined to use the damn thing! If I'd have run into this problem back then I'd have been totally stumped.
So, does my theory make any sense?
Do we have any Fireface users in a position to test it out on their systems?