Just installed a bluesound node 2i , quality not so good

Pretty funny what goes around...lol
Back in the 90,s we were using fiber optic comms for industrial usage, I liked it a lot as no noise, the "wiring" could be routed anywhere even 360 degree loops etc with zero issues.
The programmers say it did not allow enough heavy duty information exchange as Profibus and then later Profinet so we ditched it and moved on.
Canbus that you now find in cars( for a few years actually) was basically Profibus that we started with in the late 90,s, early 00,s . Profinet is really just a variation of ethernet.

Now it is showing up as the latest audio "darling"

Pretty interesting tbh.
Good luck.

superstoked, does this "tweak" still require a "hardwire" connection to the router using the fiber optic cable instead? I'm not following how it addresses the scenarios where the hardwire connection to the router is not possible due to location logistics.   

https://darko.audio/2018/08/ethernet-or-wifi-which-is-better-for-high-end-audio-streaming/

This article explains the process better than I’m able to do. There are many other articles also on the subject online. So to answer your question, yes this is a “hardwire” connection. I also have the issue of my router being in another room, and much to my wife’s chagrin, I have optic cable running across a hall and under a foyer rug. However this isn’t  the first time I’ve caused her distress with my audio hobby. I will eventually pull cable up into the attic and down inside the wall to my rig, but I live in Florida and I’ll be damned if I’m doing that in late August/September. So as best as I understand, the advantages of the bridge are as follows:  one being a much faster data transfer than WiFi, two it galvanically isolates the connection, and lastly eliminated RF/noise from long runs of Ethernet cable .

Try connecting the Node2i with digital, toslink or coax instead of analog to the Marantz.

I'm not following how it addresses the scenarios where the hardwire connection to the router is not possible due to location logistics.

It does not.
In fact you now have two extra powered devices, the sender and the receiver for the fiber optic cable.
You still need to run the fiber optic cable so if you have problems running a hard internet line due to logistics this is not going to be any different.
However it should be better than wifi and possibly the hard internet line if you can run cable .

I guess I could as I ran a new cat7 75ft cable from my server upstairs down to a new unmanaged switch downstairs in my music room.
Could replace the internet cable run with fiber optic but I doubt I am going to try at this stage