jiannu
I have a Logitech z5500 for my PC that I have it hooked up with an optical audio cable to my sound blaster sound card. Now my PS5 is hooked up to the same PC monitor (LG c4 48). When playing PS5, I just use the TV sound via HDMI. I wanted to know if there is a way to get both my PC and PS5 to work with the Logitech z5500 system.

 
 
 
Logitech Z-5500 review: Logitech Z-5500 - CNET(excerpt) The Logitech Z-5500 Digital has an impressive assortment of jacks that allow you to connect up to six source devices simultaneously. The control module's rear panel boasts optical and coaxial digital-audio inputs as well as three 1/8-inch analog minijack inputs. You can configure the three minijacks as a group to connect a 5.1-channel PC sound card or independently to connect up to three separate stereo sources. The control module's side panel hosts a 1/8-inch headphone output and a 1/8-inch auxiliary input for playing a device such as an iPod. We've seen home audio receivers with fewer inputs--a testament to the flexibility of this setup.
(end excerpt)
 
Did you review the manual/ guides? 
If so, what have you tried?
 
Manual https://download01.logite.../support/13099.1.0.pdf
 
Getting Started - Z-5500 Digital 5.1 Speaker System

https://www.amazon.ca/DSD-TECH-SH-AU02A-TOSLINK-Coaxial/dp/B0CL5XJPGC/ref=sr_1_30_sspa?adgrpid=1357898330868697&dib=eyJ2IjoiMSJ9.KJfEplq2zBqYJIbYLqxVvy844m1no8c8wH9XCqRhFPNsLJvfVzn7utq4gJposuZ2p1pU2EKZhZVq_wyD5rRdtT3ovCTJ7LxEVHKheDvWbTxEsWX-bjuY3rtzlk_NsQ79X8-EgcZPnWVq8tAAlAbIaayoNnMlIt_83i5ojfc8pT3Hkj1JmwXt-klG4TM1oge4-TMWE_RF6xPsHDnQV1xd_jbprCqPfWMeIoLDdJJmkUetD-f-FedtntQ0fSITtsniMnBrWSWUrmUMtHj-zxoJ0KvWRq7wPZTu1e84g2W7wVE.gmSw_miAlxchRaKjZae0VzLnFwnk90XJUnYF0q_XCgs&dib_tag=se&hvadid=84869107900585&hvbmt=be&hvdev=c&hvlocphy=5175&hvnetw=o&hvqmt=e&hvtargid=kwd-84869537543997%3Aloc-32&hydadcr=1282_13638339&keywords=coaxial+adapter&msclkid=144cd35c4d8b1791b1b9b4207919da8e&qid=1736193181&s=electronics&sr=1-30-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9idGY&psc=1
 
I found this... Do you recommend?

If I am understanding I think you can just connect your monitor to the Z5500 control pod with an optical cable. Since your PC and PS5 are both connected to the monitor (I'm assuming either via HDMI and/or DisplayPort) the audio should then "pass through" the monitor via the optical cable to the control pod. Might have to change a setting on the monitor but that sounds like the solution.
 

jiannu
Yes. I've tried that and it worked. Only issue now is the sound card is doing absolutely nothing......lol

Ah, that's the audio conundrum. Well if you want to utilize your sound card you could try an optical/toslink switch.. here are a couple options I found on that jungle website so pick whatever flavor you like the most if you go this route:
 
https://www.amazon.com/LiNKFOR-Digital-Aluminum-Switcher-Blue-Ray/dp/B07MPX1B7D
https://www.amazon.com/HDSUNWSTD-Digital-Toslink-Splitter-Blue-Ray/dp/B0C1RFWWR9
 
Just need to connect the optical cable from the monitor to an input on the switch (for the PS5) and then connect your sound card optical cable to another input. Then the SPDIF OUT connects to the Z5500 control pod. Sure this adds an extra step of selecting the audio input on the switch but shouldn't be terribly difficult (they even come with remotes)
 
BTW I responded to this because I too have the Z5500 and for many many years it has been amazing.