Alright, so after doing some testing, I've found a combination of items that work, in case anyone needs this in the future.
For the mixer, this 4-channel powered mixer performs exactly as advertised. I was able to play music from 2 different computers while also getting audio from my PS5 via my monitor's 3.5mm jack. Able to freely adjust inputs with no issue. I've also used the 2 channel powered mixer in the past,
That being said, there IS a substantial amount of static on the lines, considering how many different devices are involved (as a refresher, port 1 is PC audio, port 2 is 3.5mm monitor audio for use when my HDMI matrix is set to output to it, which itself has 6 console inputs and 2 different outputs, and port 3 is my work PC) there was bound to be some kind of weird feedback loop static nonsense.
To FIX that, I took a chance on this noise isolator. Used it for ports 2 and 3, only distortion I get now is when my phone is near everything and get some kind of signal. Part of me wonders if I could resolve that by just adding more isolators but it's not really a big deal to just not have my phone on the desk if it starts getting cranky.
I've mainly been working with ports 1 and 2, trying to avoid having to use the new PC for port 3 because I honestly just don't feel like it. Been getting bugged more to make sure everything works, and for my money this combination of mixer and isolator do exactly what I want them to do. Unlike with my previous 2 channel setup without isolators, I can max out every dial and volume knob involved and it be loud enough I actually want to turn things back down to preserve what hearing I still have.
So if you're looking to combine audio sources for use with 1 set of headphones, As long as you have 4 or less inputs to work with then for my money this combo should do what you need. Hopefully this helps someone in the future, since no one else was familiar with what I was trying when I was looking.
Might be a ground loop. Grab one of these. BESIGN Ground Loop Noise Isolator... https://www.amazon.com/dp/B06XQYN77L?ref=ppx_pop_mob_ap_share
Thanks for your reply! Someone recommended I get one if these:
BESIGN Ground Loop Noise Isolator for Car Audio/Home Stereo System with 3.5mm Audio Cable https://www.amazon.com/dp/B06XQYN77L/ref=cm_sw_r_awdo_6CW29RQG8P1NYQ8QXR9A
Is that what you were referring to when you said there’s a device I could use?
You most likely need a ground loop noise isolator. I don't know the full story behind it but its about being on the same power circuit as the source, PC, etc. You can easily test this by using an ext. cord plugged into a different circuit/outlet. If you get no noise or at least it is lessened, then that is it. My X4 is plugged into my PC via the included USB-C to USB-A and the line in is to my monitor which I have my Switch dock connected to (sound via HDMI). I would get annoying static just on the normally silent home screen.
This baby solved my issue:
https://www.amazon.com/dp/B06XQYN77L?psc=1&ref=ppx_yo2ov_dt_b_product_details
You will still get noise when all the way up but that is natural of any headset/speaker at eardrum bursting volumes.
It's ~$10. There are other options, mostly around $10, some much higher because of reasons.
P.S. You don't need USB-C to USB-C unless there is no other option on your source PC, laptop, etc. You're just wasting that high-speed port on something that probably doesn't need even USB 2.0 speeds.
Okay cool, I’ll give it a shot. I found one on Amazon for about $12.
BESIGN Ground Loop Noise Isolator for Car Audio/Home Stereo System with 3.5mm Audio Cable https://www.amazon.com/dp/B06XQYN77L/ref=cm_sw_r_awdo_6CW29RQG8P1NYQ8QXR9A
Would this work or did you have something else in mind?
Your comment is extremely helpful. Im first going to provide the deductions I've made, add some detail, and end with the solution.
I think I've been able to deduce it's not the second PC's motherboard, because that PC is HDMI'd to a TV. I have tried 8mm from TV >> MAIN PC or second pc >> main pc and I get an identical sound. They are on different outlets.
My main PC motherboard is relatively new and not cheap, along with most parts on the main pc. I can't imagine its that.
Can’t you share audio digitally between the PC’s? Maybe your pc’s have a toslink in/out?
I have a few apps I run through like Stardock Acoustic Bridge or Soundit, when running a VPN, and firewall, they all struggle to stay consistent.
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If I understand this section correctly,
The whining most probably is ac interference on the circuit that does the digital to analog conversion. there is a headphone amp circuit there that is even more prone to interference. Another solution would be to buy a simple d-a usb interface for your second computer.
This seems to be the most likely problem, would a DAC or this be a good solution.
i got the besign one off amazon and it has good ratings but idk maybe it just doesn’t work?
Buy a few of these, they will change your life:
https://www.amazon.com/BESIGN-Ground-Isolator-Stereo-System/dp/B06XQYN77L/
It might have to do with your extension cords. I would advise you to plug as many pieces directly into the wall, namely monitor/pc both into the wall socket directly. If this is not an option then try one of these grounding loops: https://www.amazon.com/BESIGN-Ground-Isolator-Stereo-System/dp/B06XQYN77L/ref=mp_s_a_1_3?keywords=Ground+Loop&qid=1673042295&sr=8-3
You need a ground loop isolator my friend
https://www.amazon.com/BESIGN-Ground-Isolator-Stereo-System/dp/B06XQYN77L
You may want to try a ground loop noise isolator on to the audio port on the docking station.
https://www.amazon.com/gp/product/B06XQYN77L/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1