There are several wizards and options if you open Sound in the Control Panel and right click at the devices listed in the Playback tab. Maybe you have to set them to default first or configure them using the Configure Speakers wizard. Otherwise I don’t know what the problem can be because at least one program at your pc’s plays 5.1 so the drivers etc are working well.
Pretty sure I went through all that but will give it another look.
Been using S2K8 full time for over a week now, so far the only issue has been the sound.