Fiber Optic isolation causing listening fatigue

I will take a different tack and say that you are now hearing more of your system and the way it sounds. From what I have heard of the Weiss DAC’s, they can be pretty detailed, and coupled with super efficient and fast Omegas might be part of the problem. This is purely conjecture on my part, as I have not actually heard these components. I think if you are hearing more of the music with optical, then there was a problem in the first place, but now maybe the optical components are adding in their own new noise. I have had good results with the Stack Audio Ethernet Regenerator, spendy, but a definite improvement.

I just installed the TP Link fiber media converters and thought it took my streaming up a big notch.  I got an LPS for the clean side and runs to my Lumin U2 Mini that goes into my PS Audio Stellar Gold DAC.  Very happy.  Can't stop listening.

The outcome varies. There’s no guarantee any of the tweaks will result in improvement. 
I owned Aurender n200 and adding the converters resulted in more of an analytical type of sound. The network implementation in these streamers is pretty robust. They reveal differences in Ethernet cables and that’s purely from a tone and sonic signature perspective. Noise is not so much an issue and the fiber conversion isn’t really necessary. 
 

Now, using my current streamer as an example, which is a network card built into the Meitner DAC, it is more sensitive and can benefit from additional filtering. I still don’t use fiber there but using a WW Ethernet cable with integrated filtering into switch and then a high quality etherbet cable into network card makes a very audible difference. 
Same applies to Roon Nucleus One - it can benefit from filtering. 
 

Trying what works best is the only way to know. 

Some of this stuff I’ve read on here is hard to believe

Well, I’m not sure what the specific issue is but this setup is a no go. This morning I listened to Miles Davis’s "Agitation." After Tony Williams’ drum solo, Miles comes in with a stacatto muted trumpet solo. I listened first with the fiber optic cable in place. The drum solo sounded out of tonal balance, emphasizing the higher frequencies of the cymbals. When Miles began playing many of the trumpet notes were just too hot. I had to turn it down. I then removed the cable and things sounded more natural again. It was a good experiement, but I’m not ready to start throwing more money at this. Down the road I may consider an ethernet filter or a better fiber converter. Or, I may just stop worrying and enjoy my stereo as is. It is pretty sweet, and I’m not sure a problem exists. I was just curious what level of detail I could conjure.