I must have missed reading this key fact in the topmost quote. Ferrite choke is not the most obvious solution anymore. My online diagnosis of "I did crazy stuff with my power" certainly made it a higher priority to remove as cause.
They can be fit to pretty much any cord or cable. I have USB that came from the factory with one installed. The name choke should tell you they may not be the ideal thing to place on an audio only adapter cable.
I guarantee your speakers were designed with onboard audio as one of the most likely sources. Phone and PC.
3.5mm port are more than good enough. Your mobo 3.5mm port does not seem to be so great for this application. Nor do I believe onboard sound card are a feasible solution with modern hardware. Your phone or PC realistically have the same or better capability. I suspect this will be hard to hear, but PCIe sound cards are in everything but name USB sound cards.
Sub $100 USB DAC might be your only feasible upgrade. Not option, upgrade. Not suggesting a devalued legacy piece of Schitt either. More sophisticated.
I respect the decision to spend zero monies is preferable. Any caroline! as clever as they seem might just unhook their front 3.5mm jack from the mobo and contrive a means to feed audio directly to or through a rear mounted 3.5mm female connector and adapter cable into their speakers.