Anybody gone from ethernet to optical for connection to a streamer?

Interested to know if it mattered? did you hear any sound changes?

my streamer has an optical input, and trying to decide if its worth converting over from ethernet?
I have an Etheregen and tried it with both Fiber and CAT and I could not hear the difference. (yes, I had only one hooked up at a time).  The Etheregen switch claims it's "moat" galvanically separates the "in" from the "out". My limited listening test confirmed this in my opinion. That said, I don't know if this helps answer your question, but you might find it useful.  
I’m a little confused are you talking about a fiber connection from your modem/ router to a streamer. If so what type of modem? I’m in the telecom industry but not familiar with any modem that that has fiber outputs only a single input. What equipment is before the streamer?
I can't speak to the optical portion of your question here - but I do know I swapped out my normal, everyday ethernet cable with an "audiophile grade" CAT 7 cable from Pangea. And it introduced the absolute worst ground loop/ hum into my system that I have ever had. (And, I'm still confused about how that happened... I can repeat this, and tried two different cables from them with the same results if anyone is interested.) The optical connection has the potential of reducing ground loop issues, but if you can't hear a hum/ buzz now, it most likely won't make much of a difference. 
Fibre is the best upgrade I have done on my streaming. The OpticalRendu is great. Ethernet direct into a DAC was about the same as my microRendu. Fibre optical was so much better than either of those 2. It was so obvious to me that I immediately bought a second OpticalRendu. I have been using both for about 6 months now on 2 DACs.

The only DAC with Ethernet that I think could be very good and challenge the Fibre optical is the upcoming AudioByte Hub (need the VOX + ZAP).

@jd55 I use this switch for fibre. 
Ubiquiti - UniFi® Switch 8-150W

No matter what you read here, listen for yourself and then decide.  This stuff is dependent on your equipment and on your environment, including the length of run from your router to your streamer, and the amount of EMI/RFI present in your home.  The equipment I use (both the server/streamer and DAC) have internal galvanic isolation and I have yet to hear meaningful differences when trying a variety of small boxes that many others say have a profound effect. 

That said, I am currently running 45 feet of fiber from my router to just before my server/streamer, where it is converted to a very short Ethernet cable, which enters the streamer.  Both the converters, at the router and at the server/streamer, are powered with linear power supplies and not the standard SMPS used in wall warts. 

I have run CAT 5, CAT 7, and CAT 8 cables and again have not noticed significant differences.  If anything, the fiber may result in a bit smoother sound compared to any of the CAT cables, or it may be my imagination.   You may want to look at the differences between CAT cables which vary in the level of shielding.  CAT 8 provides the highest level of shielding and could offer an improvement in noisy environments.    Both the fiber cable and the converters are inexpensive so try for yourself and let your ears decide what sounds best for your gear and environment.