You mark your favorites by pressing whichever key you have defined as the Add Favorite button on the Setup 2 sub tab of the controller tab. You switch to your favorite list by pressing whichever key you have defined as your Toggle Favorites list.
You might have trouble if you trampled the built-in feature by making your own game list called Favorites.
BTW, Maximus Arcade is the front end. X-Arcade is an arcade parts company. (although neither of them can be bothered to support this abandoned garbage.)