Why do I need a switch?

Always the naysayers.  Too funny.  I got me an expensive network switch, put it after my fiber media convertor and got an improvement in sound on the stereo.  Mostly, the bass improved.  So then as an experiment I bought a 100ft Cat7 ethernet cable and patched it from my new network switch to the TV in the family room.  Wow!  Quite the improvement in picture quality.  If hearing isn't believing, seeing must be believing.  Then, since my TV was previously streaming via wifi and an Apple TV box, I plugged that Cat7 ethernet cable into the mesh repeater near the TV. The TV picture quality improved almost as much as when I plugged the Cat7 cable into it directly.  Spent a good half a day running ethernet cables from my stereo Network Switch through the walls, under the house and to both my TV and the mesh extender.  Well worth the trouble, I found.

Perhaps.  Before I added the ethernet cables and running just wifi, a speed test on my TV would show >250mps.  I consider that a pretty good wifi signal.  Keep in mind that the main router is connected directly to the modem.  I am using a wifi 6e mesh system with the secondary router close enough to have a full strength signal.  

I ran the ethernet cable to the secondary router out of the audio grade network switch.  95% of the picture improvement was via wifi from the secondary router to the TV after adding the ethernet cable from the network switch.  The additional small improvement came by connecting an ethernet cable directly to the TV from the network switch.

After connecting the secondary router to the network switch, wifi speeds increased to 550 mps in the room with the TV.  

So you added optical fiber in the Ethernet chain from your router to your music server?  Anything else between the router and your music server?

And you hear no difference?  Well, I’d say that you should have heard a difference immediately if you were going to hear anything.  It’s likely that it will not change over time.

So you are using some type of Wi-Fi device?  That changes the game.  

1) Put the fiber section between the router and the Powerline device and see if that sounds different.

2) Try to run an ethernet cable from your router to your music server with and w/o the FMC’s in the chain- if you can to compare the sound.

I bought a long ethernet cable and ran it from my audio grade network switch, which is after the FMC’s, to my TV at the other end of the house.  The picture looked so much better that I ended up working 6 hours running that cable through the walls and under the house to the TV.  Running an ethernet cable to the 2nd mesh router at that end of the house made the TV picture just about as good but since I had to run one cable to that end of the house it wasn’t much more to run two.

Everyone has differences in their systems and not surprisingly have differing results.  I try to normalize my streaming results by comparing it to my other sources.  I have four different sources now: Vinyl, CD, FLAC files stored on my music server and Qobuz.  I'll stay away from vinyl for now.  So on the digital side I am using a CD transport and separate DAC.  Then I have a music server with USB to the DAC.  I ripped my CD collection into FLAC files stored on my music server.  After trying a couple of different USB cables I'd say that my CD to FLAC files are very close in sound to playing my CD's directly.  I did some back and forth but mostly I like to listen to a song and then play it again from the other source.  I am satisfied that to me the music server and CD transport are very nearly the same.  I use ROON but do not use any oversampling or conversion.  I have ROON set as basically a pass through with PCM output to my DAC.  I tried DSD output with various filters but never sounded as good as direct PCM out.

When I started streaming I was using an ethernet cable from my router directly to the music streamer.  Streaming 16/44 was clearly less than CD quality.  Then I added a cheap network switch and heard some improvement.  Next, I tried FMC's and found fiber was a good upgrade in the sound.  The differences between streaming 16/44 and CD was getting smaller.  I took out the cheap network switch and found that was an improvement.  Next added the Finisar 1475 SMP's (these are the plug-ins found on the FMC boxes) and got a nice improvement.  At this point 16/44 streaming was very close to CD and hi-res FLAC files vs streaming hi-res was also very close.  Finally, I added the LHY SW-8 network switch after the Fiber and changed to Pangea ethernet cables.  I hear no difference now between spinning CDs, FLAC or streaming.