These are usually two different cables, for sound either you use hdmi sound transmission or you use a dedicated optical spdif cable just for sound. I have never seen a cable combining the two.
Desktop : Intel Core i5-750, 4GB RAM, ATi HD5870, Windows 7 64bit
Laptop : Intel C2D-P8600, 4GB RAM, nvidia 9700M-GT, Windows Vista 64bit
Displaying Zalman Trimon 22" and 106" Passive polarised dual projector setup.
Watch my Stereo3D gaming video footage viewtopic.php?f=3&t=2020