What is it that you are trying to do?
Someone with more knowledge will hopefully provide a suggestion in regards to the FMCs. Ironically, I did a deep dive on optical last night. I found threads from WhatsBestForum (here, here, and here) pretty helpful, as well as some from Audiophile Style.
I think the question I have as a follow-up for the community is whether or not that "active" optical cable may also be causing an issue - I candidly don’t know, but I vaguely remember reading this as an issue in one of the threads above.
Like you, I’m still learning while regurgitating some of the information I had been reading last night. I'm pretty confident more members will contribute to help figure this out. As a side note, I've found one of the easier paths is looking at Small Green Computer's solutions, which can be found here and here.
I would have stuck with something simpler, that has the media converter built in. Keep in mind that 100 MBits is overkill for any streaming of audio or video. 1 Gbit (1000 Mbits) is overkill x 10.
A 192k/24 bit stereo signal is barley 10 Mbits. A 4K video stream requires around 50 Mbits or less, depending.
So, a 1 Gbit/s cable can carry 20 4k video streams at once.
Maybe that can help you pick out a better integrated adapter and cable such as:
@brylandgoodman This is what I use for my two systems and it works great. Lps is optional but better than wall warts. Small green computers is excellent but more expensive if that matters. I own their sonic transporter it is fantastic.
I can't really figure out what he is trying to do... not sure why he isn't plugging the ethernet cable into the modem and the modem into the computer. There are multiple programs you can work with directly on your computer once they get there that should do whatever it is he wants to do and unless I missed something, a lot simpler.
Back up first and be sure everything works in copper. Any old dirt cheap CAT-5 cable will do. Actually it will do as well as any snake oil "audio Ethernet" cable. Ethernet and TCP guarantee every bit is right. Everything is buffered so no magic timing differences.
Then test/listen to the system and see if you have a problem in the first place before you add band-aids for problem that does not exist or think you can magically get sonic improvements. You won't within the laws of physics in this universe. I know, some here seem to be in another universe with different laws where the IP stack is analog.
Optical transceivers should be totally transparent to the computer/router/switch etc ports. They just convert bits to bits and do nothing to the protocol, unless newer venders have found ways to screw things up. The transceivers we used were st connections for multimode fiber and did 1G E. I can't remember the brand but they were cheap and reliable. Grey box. Multimode and single mode fiber are not interchangeable.
I do not understand why an "active" optical cable and also list transceivers. You should just need an SPF cable.
Some folks just enjoy being disruptive. It's as when a guy asks for a phono cartridge recommendation, and a user tells him to get a streamer instead. Or the guy here who recently asked for DAC advice, and was told to buy a 4K TV and an "object based" sound system instead.
Dolby Atmos is a digital standard for both audio and video that works on all platforms and is backward compatible. Why would I want to BUY multiple sources, dacs, and preamps today that will be boat anchors within five years? Buy one box and a firestick and you are done, keep the change thank you very much.
@kota1 - "Why would I want to BUY multiple sources, dacs, and preamps today that will be boat anchors within five years?"
What hi-end manufacturers are you seeing divorcing themselves from 2 channel audio that this is going to be the case?