Like Thom said, big system! I would suggest getting your head around the DCE concept to begin with. Thom mentioned it, but it isn't necessarily obvious what this is at first glance. There is a basic diagram on the wiki somewhere. But essentially, LMCE all hangs off a messaging architecture.
The DCERouter is the "hub" if you like, that all messages (commands, events, etc) are switched through. Practically all functionality is implemented as "DCE Devices" (that you can see in the web admin). Each "device" is a software "module" that can open TCP connections with the DCERouter, and use them to send/receive DCE commands and events with other DCE Devices. A device isn't necessarily hardware, for instance the functionality that actually plays audio and video media is the Xine Player device. This is a piece of software that can receive DCE commands from the rest of LMCE and uses the xine libraries to play the media.
The OnScreen Orbiter is also a DCE device, and can communicate with the others as well. So it uses the Media Plugin (a house-wide embedded DCE device within the DCERouter) to create a house-wide media stream object, that can then be used when sending a command to a Xine Player device, so that Xine Player plays that stream. As this is a house-wide object, you can then instruct the media stream to be moved to another Xine Player on another Media Director, and playback will move and resume in the new entertainment area. This is all done with the DCE system.
Many devices are simply conventional GPL applications/packages, that have been wrapped with a DCE communication layer. In this way, the LMCE system can implement almost "virtual" commands like Power ON/OFF, and send them to any area, or the whole house - LMCE doesn't actually need to know how to turn the power on or off on a specific amplifier, TV, or lamp, when the DCE Power ON command arrives at the DCE device responsible for controlling that piece of equipment, the DCE device receives and interprets that command, and takes the appropriate action to execute it. Thus LMCE is a "framework" system as well. So for your application, you would want to know how to build a DCE device around the functionality you want to implement and determine which DCE commands are appropriate for you to implement.