I am trying to figure out how to convert my 3 3.5 mm analog wires to an optical. my setup is the cheap little 5.1 set by logitech. meant for computers obviously. My comp has no optical audio port and i just got a ps4 i want to be able to use true 5.1 with my ps4 for blu ray playback and gaming somehow. I was wondering if there's some kind of conversion for an otical out to splice into those 3 analog cables or if theres a way to use my comp like a reciever. currently I'm using the traditional 3.5 mm headphone patch cord from my ps4 controller to an audio in on my pc. but that just uses speaker fill it's not actual 5.1. thoughts? the set of Logitech speakers i'm using is the Z506 set.
If I understand correctly, what you are looking for is a DAC (digital to analog converter), to convert the digital signal from the optical output of your PS4 to a multi-channel analogue signal to use with your computer speakers. A six (at least) channels DAC.
Most of those DAC, are, however, stereo only. To my knowledge, only a few multi-channels DAC exist and they won't be cheap. Some digital home theater receivers might have that feature, but once again, that won't be cheap either.
Considering the value of your speaker system, neither option is probably worth it.
I'm afraid there isn't a simple solution to that issue, unless you are willing to spend a few hundreds dollars, at least.
Edit: did some more research, and it seems that some of those DAC can be had for much less than I expected:
(I cannot guarantee that this particular product will work for your purpose, you'll have to read the reviews.)
Be careful with the one you listed from ebay, though. I saw a similar model on Amazon. If you read the details, it states: "Digital Optical Audio Input: for recording digital audio from audio receiver, amplifier, mixer or recorder and saved in computer files for playback or disc production.", which I think means that you need to use USB with this one if you want to output to 5.1, the optical-in is only for recording.
Also this: "This usb audio converter transforms ordinary mono or 2-channel PC audio with expanded sound fields to deliver the excitement of surround sound content." Which does not inspire confidence as to its ability to handle 5.1 channels at input.
I'd do more research on this one before buying, even if it is significantly cheaper. There might also be other options on Amazon, but pay attention to the reviews before making your choice.