How to use Big Picture Mode with Chromecast and Vader 4 controller?

[JDub]

Moonlight running on Chromecast connected to Sunlight running on gaming PC. I'm using a Vader 4 controller, which is great, but I can't figure out how to access the Big Picture menu from the controller. Anyone have a suggestion? I can start BP mode on the PC and then pick a game with the controller when I'm sitting on the couch (different room) but I can't get back to the BP menu.