Let me start saying I haven't read this entire thread but I have read others and I do believe people have heard an improvement with optical interfaces vs ethernet.
I'm also aware SGC and Sonore make exceptional well regarded audio products.
That said it is a misconception to think optical as a technology is "completely" clean for RFI purposes, now if this RFI dirtyness (residual of optical) affects audio or not that's another story.
The entire RFI/EMI issue arises on ethernet and dacs, servers and such on poorly designed and improperly shielded systems. When you are modulating a wavelength (either multimode light or single mode laser) over fiber there are residual RFI which by the way are many times higher than with actual ethernet, 30 to 40 dB in magnitude, radiating in all directions and inducing into cables creating antenna effects everywhere, shielding with aluminum, copper and even cable shielding blocks at most 10 to 15 percent of this signal but it is ineffective at blocking effectively specific residual due to their magnitude. This problem is even more accentuated with BiDi devices which transmits and receives over the same fiber on different wavelengths. Finally this will get induced into ac adapters, other cables and such.
Does it affects music? Apparently not since no one has complained and people I trust have tested the Sonore and SGC products and report an improvement with optical, but it does exist and it is not "completely clean"
On my testing some optical equipment is better than others blocking and shielding this effect, SGC and Sonore products haven't been part of my testing as my test was on a different application than audio related directly to my work.
I'm also aware SGC and Sonore make exceptional well regarded audio products.
That said it is a misconception to think optical as a technology is "completely" clean for RFI purposes, now if this RFI dirtyness (residual of optical) affects audio or not that's another story.
The entire RFI/EMI issue arises on ethernet and dacs, servers and such on poorly designed and improperly shielded systems. When you are modulating a wavelength (either multimode light or single mode laser) over fiber there are residual RFI which by the way are many times higher than with actual ethernet, 30 to 40 dB in magnitude, radiating in all directions and inducing into cables creating antenna effects everywhere, shielding with aluminum, copper and even cable shielding blocks at most 10 to 15 percent of this signal but it is ineffective at blocking effectively specific residual due to their magnitude. This problem is even more accentuated with BiDi devices which transmits and receives over the same fiber on different wavelengths. Finally this will get induced into ac adapters, other cables and such.
Does it affects music? Apparently not since no one has complained and people I trust have tested the Sonore and SGC products and report an improvement with optical, but it does exist and it is not "completely clean"
On my testing some optical equipment is better than others blocking and shielding this effect, SGC and Sonore products haven't been part of my testing as my test was on a different application than audio related directly to my work.