They were just modules that plugged in to the spdif header on the card. If you dont need optical, then all you need a header, two wires and an rca socket
The module I had plugged into the digital 3.5mm socket, rather than header on the card.
I imagine the same thing would work from the 3.5mm socket in the same way it would from the header.
Alternatively, could anyone recommend a cheap sound card that has a coax digital out. I’ve seen a few but they need two empty expansion bays and I only have one.
SB Live! 5.1 has/had the same digital 3.5mm output as the Xtreme Music I had.
The module plugged into the 3.5mm digital socket and allowed for either coaxial or optical to be connected. Not much difference from using the header as James described for coaxial; two wires from the SPDIF header to an RCA socket.
That 3.5mm to coaxial RCA cable should work in the same way from the 3.5mm digital socket, so I'd try a cable similar the one you linked to. I'm not sure why that one has a three pole stereo jack though. Coaxial is just two contacts; signal and ground. There's a Gotham one on eBay which has a two pole mono jack. Similar price to the Micca cable.
It should work, but what you could is get a cheap piddly thin 3.5mm to RCA mono cable, which is the same thing, just extremely thin with no shielding. At least that will tell you if it will work and spending more on a better cable is worth doing.
As for sound cards; I don't know of any cheaper ones with coaxial output. Except for cards like the Xonar Essence and Soundblaster ZxR, I thought that connection type has pretty much disappeared; although maybe it is still used on cards intended for music creation.
Sound card with optical, and an optical to coaxial converter is one way to go about it.