RetroArch

Setup with LaunchBox

Open LaunchBox
Go to Tools -> Manage... -> Emulators
Click Add to add an emulator.
In Emulator Name dropdown choose Retroarch.
Application Path doesn't have to point to real application. It's enough to just input retroarch.
Click Associated Platforms, and make sure "Default Emulator" checkbox is checked for platforms which should be started with Retroarch.
Optionally, if you need to set up a different core for a game, go to Launchbox, select the game, open "Edit Metadata/Media" and modify command line under Emulation.
For seamless experience, it is recommended to setup a hotkey for quitting RetroArch. When content is started from RetroPass, once user exits RetroArch either with the hotkey or through the menu, it will immediately return to RetroPass.