S/PDIF doesn't support that kind of 8 channel output, I believe that would only work on the HDMI output of the motherboard (or from the analog outputs on the motherboard).

You might also look at Dual Disc format, at least they only cost a couple dollars more than normal CD's, but contain a DVD side with surround and hi-res stereo tracks (on most). Though there aren't that many Dual Disc CD's.