XLobby (free :angry: ) not MainLobby.
Warning: Slightly convoluted, but 100% reliable (and fast).
XLobby has a very nice (free) plugin for the Elk M1. From this plugin I can control all the Elk outputs; 4 of which I have set up to feed into the GV-NetIO card. The NetIO card has 4 inputs (controlled by XLobby via the Elk), 4 outputs that XLobby can read from the Elk, and RS485 control (for camera PTZ functions).
Geo recognizes the Net-IO card, and has an I/O configuration window that allows you to "assign meaning" to the I/O items (just basic stuff like preset zoom, alarm outputs, trigger recording, etc). From the items above, that is how Xlobby can "control" my Geo system.
Now, your question may have also meant to ask how XLobby can display the Geo live or recorded feed. In both cases, I open up a browser window and point the browser at the IP address of my Geo machine. I only open a partial browser window (XLobby still shows on one side of my screen), and leave room for my X-Lobby buttons that I have built for whatever my IO button are programmed to do.
Geo has a NICE built in web server that provides you with multiple different options.
Hope this help