If you already have the iMON remote software installed, all you need to do is press the mouse/keyboard toggle button right above the up/down left/right joystick. If the mouse moves on the screen when moving the joystick, you are in mouse mode. If it doesn't, then you are in keyboard mode. When in keyboard mode, the joystick and enter button can completely control MC in Theater View without any additional programming. You can set the default for mouse mode or keyboard mode in the iMON software by going to iMON Manager>Settings>Remote Control and then under "Initial Keyboard/Mouse" select "Keyboard."
To add more buttons for controlling, search in MC's help for hot-keys and you will find the list of all hot-keys for controlling MC. Any of these can be used by the iMON remote. To add a button command, go to iMON Manager>Settings>Program Commands. Use the drop down list to see if Media Center 12 is listed and select it. If it isn't listed. Click "Add Program" and browse to Program Files>J River>Media Center 12>Media Center 12.exe and add as a program.
Now click "Add" at the bottom left of the screen to add button commands. Type "Play" as the name of the command and click next. Click into the left box for entering hot-keys and press the left ctrl button. Now click the middle box and press P and then next. Now select the remote button from the drop down list. The one you want will probably be (IMONPAD)Play. Click finish and you are done with that command. I also add the same command in and then select (IMONPAD)Pause, too. This way either the play or pause button will play or pause MC.
Here are a few other helpful buttons:
Next Track Left Ctrl + N (IMONPAD)Next
Previous Track Left Ctrl + M (IMONPAD)Prev
My Music Alt + 3 (IMONPAD)Green
My Photo Alt + 4 (IMONPAD)Blue
My Movie Alt + 5 (IMONPAD)Red
(I can't quite remember, but I think the button name for the above was just the color. Also, the color buttons only work in Standard View. They do not work in TheaterView. I have made a request to MC to allow them to work in TheaterView, too.)
You can also add the buttons for Forward, Rewind, Stop, etc. for use when watching a movie.