I started from scratch again. This time I tried Pinball FX2 specific instructions but now Rockerlauncher does not give me the option for Pinball FX2.
The RocketLauncherUI plugin for PinballX must be updated to show the Pinball FX2 system.
As a work around meanwhile you could create a custom system, name it as Pinball FX2, and keep it disabled.
Brolly, when the RocketLauncherUI plugin for PinballX was made, there were only two predefined systems on PinballX (Visual Pinball and Future Pinball) and all the others should use the custom ini systems structure. Right now PinballX has an extra predefined system, Pinball FX2, so you should update the RocketLauncherUI Plugin to look for the Pinball FX2 settings on the ini file, under the [PinballFX2] section, like you are already doing for the Future Pinball and Visual Pinball systems.
Here is how my PinballX\Config\PinballX.ini file looks right now if it helps you to understand the changes:
http://pastebin.com/LkHQ6XUJ
Edit: pastebin link updated to point to the correct file.