Connecting a Creative PCIe Sound Card to 7.1 Speakers

I recently bought a Creative Sound Blaster Audigy Rx sound card for an application requiring 7.1 audio. It's a nice sound card, installed without any problem. However, when I came to wire it up I hit a snag. 7.1 audio requires eight separate sound channels. I had assumed that the card would have four stereo jacks to carry these eight channels. Nothing so logical; they use one stereo (3 pole) jack for two channels and two 4-pole jacks for the other six!
To make things worse, the card does not come with a cable to allow the card to be connected to a 7.1 speaker system. Creative apparently used to sell such a cable as an accessory but it is now unavailable, and nobody else makes one.

Luckily the manual for the card shows the pin-outs of the audio output jacks.
Also luckily, these 4-pole jacks are commonly used for other things, such as carrying stereo plus composite video signals from DVD players and suchlike, and you can get cables with a 4-pole jack on one end and three RCA phono plugs on the other.

So to connect your 7.1 sound card to a surround-sound system with 8 RCA phono sockets, you'll need one standard 3.5mm stereo jack plug to two RCA phono plugs cable, and 2 3.5mm 4-pole jack plug to three RCA phono plugs cable.

Don't forget they have to be 3.5mm jacks, not 2.5mm ones!

And here's how to wire it up. A 2-plug cable is stereo and a 3-plug cable is the one with the 4-ring jack. The colours refer to the phono plug colours. The ground connection on each of the jacks goes to the screens of all the RCA plugs.

If you want to connect the sound card to equipment that has something other than RCA phono inputs there are plenty of audio adapters out there.

I hope this helps someone get the best out of their sound card.