Thanks to all who responded - I downloaded the later version of SonicStage: unfortunately I can't find any drivers for W7 or W10, but I successfully installed it on an older laptop running XP, so it's another string to my admittedly alopecic bow.

I'd forgotten about SPDIF sound cards, in fact I was looking at them before I settled on the USB route instead: they could still be a fallback as I have a couple of MD decks with optical output.