My Sony DAV-HDX589W is connect to my GA‑Z97X‑UD5H‑BK motherboard with a digital optical cable. I can only get the 2 front speakers to work. I tried adjusting the S/PDIF properties but I only get an option of 2 channel audio. I'm pretty sure all my drivers are up to date. Any help would be greatly appreciated.
either your receiver or motherboard doesnt support 5.1 over optical or your receiver doesnt support the standard (like dts-c, ddl) that your pc can output.
it wouldnt surprise me if your receiver doesnt support 5.1 inputs as this is fairly common (and a big reason i do not suggest htib's) on cheaper home theater in a box (htib) sets though i'd check your manuals for both motherboard and htib to verify.
if your receiver supports it but motherboard does not, a cheap soundcard would work, though sometimes driver updates add the feature (though you say you are already up to date). if your htib does not, then sorry there is no fix for that (other than upgrading the receiver to one which does support it).
in short: first thing to do is read the manuals to check if they actually support 5.1 over optical. the default answer here is "no, they support stereo only" as the only way to get 5.1 is via compressed audio (ddl, dts-c for example) and if both devices do not support this compression you will not have the option.
Do you have another digital source to tell if you have the SONY set correctly to decode for your surround speakers? The digital out should be passing the signal.
In windows, right click the volume icon. click playback devices. Make sure the output device is set to the optical out. In the lower left is the configure button that would let you select the 2-channel or 4-channel or 5 or whatever if you were doing the decoding in the PC, but you are not so the configure button is probably greyed out.
Soem cross checks: Connect an HDMI cable from the PC to the Sony and disconnect the optical cable. That will send the same signal over the HDMI as your were sending over the optical. If it works now its in your PC settings. If it doesn work then it's likely in the Sony settings. The HDMI audio does not use your MB audio chip, it uses logic on the video card.
Here is some sony debugging. It might help: https/us.en.kb.sony.com/app/answers/detail/a_id/31317/c/65,66/p/46871,74233,75026/