Is fiber optic internet

Lot of theoretical there Jim @jji666 I have both Fiber to my house and a fiber home network (I converted) and it was a night and day difference in performance and quality. Nothing theoretical about it.

It is all about the converters... light to electrical. The rule of thumb used to be no because of the cheap optical to electrical converters. Only occasionally now yes, because of audiophile quality optical to electrical converters. Otherwise high quality electrical filtering and isolation is better. 

Firstly, the difference that may or may not be heard changing between copper, fibre and wifi seems to depend alot on how revealing your sound system is, how low the noise floor is, and how noise each network device generates.  I am quite sure the noise that a network device experiences (input and self generated) affects its performance and 'somehow' can affects sound quality.  This is based on heaps of experimenting with a range of audiophile and generic network devices, cables and tweaks.

I am quite sure coax internet service will most likely transmit more noise into your devices than fibre, far more than the SFP module.  The first device (optical termination) may add noise to effrct8ve reduce the benefit of fibre.

Then, your network devices add more noise baxk,such as switches and Fibre media converters can add noise back.  Then cables collect some noise and transmit it in your network.  Network isolation transformers  (in switches, routers) seem to do little to block noise, fibre seems to block more.  In my experience, it is worthwhile trying to optimise every device, power supply and connection (cable, etc) in the network, especially in the direct route from internet to streamer.   It can be costly so try to keep perspective and commensurate with the calibre of your other gear.

I have fibre optic internet service, SFP+ router, fibre, and finally wifi  connection to Mt Devialet ... so I'm not an advocate for any particular medium, moreso an advocate to use whatever gives the best value solution for each connection.

Fibre is great value for long runs where $1k per metre for audiophile cable is not feasible/good value.

@rivinyl 

My wifi was not performing well, so, I went to a EERO mesh system and my favorite and most performing configuration was using a short ethernet cable from an EERO mesh node next to my streamer, then, that EERO mesh node goes wirelessly to another EERO mesh node connected with another ethernet cable directly to my router.  This setup was a game changer regarding the stability and performance of my wifi. This enabled me to turn off the wifi on my streamer which could be a source of noise and also enabled to use a stack audio smoothlan network filter infront of my streamer.
Also, I have copper (DSL) coming into my house instead of fiber optic, so I got rid of the line noise before going to my mesh node wifi or equivalent by converting to fiber optic and back to ethernet.  Here is a pic of what my conversion looks like - starting from my router, ethernet to fiberoptic, back to ethernet, then to my EERO mesh node that goes wirelessly to the EERO mesh node next to my stereo which connects with ethernet to my network filter and streamer.
I use a linear power supply (5 volt LPS) to power the EERO Mesh node near my stereo which is connected with an ethernet cable.  In fact, I use multiple LPS to power all my 5 volt stereo components.  All my stereo components & EERO mesh node are on the same AC circuit all going through (except my tube monoblock amps) the same Shunyata MPC-12 power conditioner.  Here are some pics.