Ideas to Implement a Game Center Module on Exsisting Web Application

I have a CodeIgniter MVC web application which works perfectly. Recently, my client asked me to add a game center module to this web application which we can add game modules as we develop them and, the first game they want to add is a backgammon.

So the game center itself is basically a new controller in exsisting MVC application, so that both game center and mvc application can share the same user session.

But for the backgammon module, which approach should I use?

My ideas:

• A node.js application to achieve peer-to-peer connection between users.
• A flash or Java / Javascript based backgammon game which can communicate with the node server.
• A Flash game, which uses Adobe's Cirrus (http://labs.adobe.com/technologies/cirrus/) to allow P2P game experience.
• A php web service like module to handle various requests from game client (in this method, game client can be written in anything)

Considering all the game modules must have a user to user chat module, which approach should I choose? What are the pros / cons of these methods, or, any other method I couldn't think of?