Two Kodi instances not seeing each other

Hello guys,
I am new to Kodi – but not to computers and networks – I looked for documentation on the following issues but could not find anything specific; instead I found a whole lot about similar problems. I hope it is the right section of the forum to ask. In case it isn’t plese accept my apologies.

So, I have just recently bought my first Smart TV box (TX5 Pro), that comes with Kodi 16.1 preinstalled. I have configured it, connected to the network and video playback works fine.
I also have installed Kodi 16.1 on my pc, and it also streams video correctly. My pc also has Samsunk Link 2.0 installed, which is a DLNA server I use to stream video files to my smart dvd player.

On both of them I have configured System -> Services -> Upnp/DLNA ->
x Share my libraries
x Look for remote Upnp players
x Allow remote control via Upnp

This should allow both instance to act as servers and clients, if I understood it correctly.
My ultimate goal is to be able to stream my pc desktop to the tv box kodi, and I know I will need some more dlna server like Serviio, but for the moment I am focused on network visibility.
With the options above enabled, I thought I should have been able to go to:

Videos -> Files -> Add videos -> Browse -> UPnp devices -> and here add Kodi instance in the other system, right?
For example, on PC I should see ..-> Kodi TX5 Pro

Well, it does not work.
Among sources, I only see:

– PC[Bestia] (which is the name of my Samsung Link server)
– Kodi (localhost)

I know it is not a network issue because in my Smart TV Box Kodi I still can see the PC[Bestia] server. So I know the two boxes can see each other because the S-Link server gets correctly announced and picked up by the TV Box server.
Yet, Kodi on TV can’t seem to be able to pick Kodi on PC and viceversa.
What am I doing wrong or missing?

Thank you so much to whoever can help!
Marco