Custom server config for simple networking.

Hi everyone. For a quick look at my problem; skip to TL;DR.

I have rather a very specific question regarding Networking in a Unity Game. First and foremost the main culprit here is all the guides direct us to using Unity's own services or Photon's services. Consider that this is not an option for this question before you provide any help. And any help provided is greatly appreciated :)

We are a group designing a turn based board game (2 people and no more) for unity and for conceptual and marketing reasons, our trailer video became a good hit in our country. The game has extremely complex mechanics and just too many data to work with. Security is a must since it's an online game or rather to put it more specifically; an e-sport. So to the question;

We intend to develop our own server for Unity network messaging. A solid and simple example would be like this: when a user does MouseOver an object on his client, it glows on the other client too.

I am sure that this is possible but what would be the best approach? We currently own a Linux server with apache support and a Windows server with .NET support. We thought that this would be the easiest to do, just simple string messaging but apparently it's not according to weeks of research. So anyway, how would this work? Could we use Unity's own networking system like the MasterServer? Or should we develop a usage for Unity as well?

BTW the game already uses our apache server for database interactioins heavily.

Some possible solutions we planned but not tried yet:

• -Completely put the wight on PHP. Try php socket handling or session handling and sending & receiving messages over wan ip's with ports. The likely problem here probably would be a problem of a firewall. But yet again, does anybody 'not allow' a game they want to play? Don't think so.

• -Put the work on a database table and both clients check it like per secs. Obviously not the best choice since thousands of gamers will be online at once. But would it still get the job done? Not even sure about that :)

• -Direct p2p connection solutions. Are there really? If this can be done, since we would be only sending and receiving just cosmetic messages (the actually important data is already being sent by a database securely encrypted) this would be our first preferance without disturbing a server. Again, the firewall issue, yet again the same answer. Couldn't explore anything about this since every single guide (EVERY SINGLE ONE OF THEM) points to either photon, smartfox or unity matchmaking. Is this possible through Unity's own backend? If it is, how would you suggest starting? MSDN or Unity's own reference?

What would be the easiest way?

TL;DR no photon, unity mm or 3rd server solution plz. We need a starting point for allowing our game to communicate using our own server. Nothing else, no bounds to no other company or 3rd party. Where to start? A rather easier way for only simplest messaging would be sufficent. Just need two clients to send or receive some strings that's all.

If anyone is willing to help us, we greatly appreciate it. If we come with a solution from a suggestion here, your name will be on the thanks section of our game if that matters too you :)