Using two controllers - 2600-daptor II and Xbox 360 to control Retroarch / Launchbox

Hello, I have a 2600-daptor II (http://www.2600-daptor.com/2600-daptor.htm) and a XBox 360 controller that I’m using with Retroarch / Launchbox. Both are working fine and are recognized in Windows 10, and are setup in Retroarch individually and are working properly.

I have a classic Epyx 500xj joystick connected to the 2600-daptor and it’s working great to play games in Retroarch when emulating Atari 2600 / 7800 and C64, however since it’s only a single joystick with a single button, I can’t control the level select or reset/start functions for Atari games. I of course can do this using my Xbox 360 controller, but I prefer playing the 2600 games with a classic style joystick.

I am wondering how I would need to configure Retroarch in order to be able to use the 2600-dapter II joystick to play games, and the 360 controller to change difficulty / reset games and navigate back to the frontend? Any help is appreciated, thanks.