Most of the computer soundcards that output spdif through a 1/8" jack use a stereo jack but only the tip and the ground are used, if you use a mono plug and do not have the souncard outputing the digital signal all the time, you may be shorting out part of the cards amplification which could shorten the lifespan of the card. I would recommend using one of these adapters which I believe you would connect to the right channel for most cards, but you may have to one or the other. This way you can use any standard sheilded RCA cable you may have, if you are running more than about 8 ft, I would recommend the rg59 or rg8 cables but are not usually required for shorter runs.