Here’s my take on it…
Every active electrical device, be it a router, a switch or a copper to fiber optic to copper converter setup (2 FMC modules) will inject its own noise into the output.
If you’re looking into a switch, the main objective in designing one for audio would be to reduce, as much as possible, the power supply noise and its digital circuitry from polluting the output making a signal transfer to the output as clean as possible.
As to the fiber optic converter setup where you have two FMC units - one converting from copper to fiber optic one converting back to copper, on the so called “clean side” of the second unit where signal is fed thru the copper into the streamer, you once again introduce all the noise you had eliminated when you converted copper to FO. Even if you use linear power supplies on the modules…they are usually made with cheap components and without audio in mind. Insert a switch into that equation or on its own, and you get the same garbage thrown into the output ethernet cable. This wont matter for pure data transfer in an industrial/commercial setting but in audio it does as it makes your streamer and DAC work more to clean it all up.
I tried that FMC set up and it didn’t sound as good as the straight ethernet or ethernet cleaned up by a Network Acoustics Eno passive system.
I also tried a cheap switch and it made things worse once again.
All this adds nothing but clutter. So unless absolutely necessary, I wouldn’t use a switch or the FMC stuff. Use a good ethernet cable from router or mesh - that’s all you need.
Before spending money on all these tweaks, invest in better quality components. No switch or ethernet tweak will bridge the gap between a low/midfi component and a high end one. No matter how many of these tweaks you throw at it. You just can’t polish the turd.
Now…if you have a streamer that accepts fiber optic input, there’s your chance to get rid of noise and interference feeding the streamer.