Quote: "However as far as I understand it, AGK's multiplayer is only for LAN..."
I've read through the documentation and it mentions that connecting outside the LAN is possible, it just needs an IP address and port to send messages. See
http://www.appgamekit.com/documentation/Reference/Multiplayer/HostNetwork.htm
Quote: "The server code doesn't need AppGameKit - it just needs to establish connections with itself as a gateway and forward messaged to session members. I've got a Windows server for development purposes, so I can knock something up test it."
That's good news that its possible. I don't have a ton of experience with writing network code, which is why I was hoping to have AppGameKit do most of the heavy lifting for me.
I'd love to hear if you could get a proof of concept working so I know that I'm heading in the right direction.