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

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

+1 @jjss49 
I went back and forth with my node from internal to external dac many, many times, on a variety of speakers. There is a difference that is unmistakable. That said, the internal dac isn't terrible and everyone has their own systems and tastes.

I agree with you hilde45, it is not horrible. I ran my Node,and then my Node 2 for a good 3 years or so with just the internal DAC. A couple of those was just with Spotify. When I moved into hi res streaming via Qobuz and Tidal,I was very pleased with the increase in sq.  I think for a lot of folks,the internal DAC is adequate. I still think it’s a great value for an all in one solution.

+5, agree with others.

The COAX OUT on the back of the Node 2i is still there for a reason.

The designers provided a good streamer platform with a decent Burr Brown 24/192 DAC inside the 2i series, and it works well as-is for most.  However, if streaming is a must and you spent good money on amps and speakers, the option is there for those who want to pair it up with a higher grade external digital analog converter.  

Connect a great external DAC to the Node2i, paired to a good amplifier and speakers, and bring the sound to a new level. The benefit of this has been discussed ad nauseam on many forums, fwiw.