Combine 2 tablespoons water and 2 tablespoons sugar in a microwave-safe glass measuring cup; microwave at HIGH 2 minutes. Stir until sugar dissolves. Combine sugar mixture, orange juice, and next 6 ingredients (through chiles) in a blender, and process until smooth. Add ice to blender; pulse to combine. Stir in 1/8 teaspoon salt. Chill in refrigerator 30 minutes, stirring after 15 minutes.
Combine remaining salt and 3/8 teaspoon sugar in a saucer. Rub the rims of 6 glasses with 1 lime wedge; spin rim of each glass in salt mixture to coat. Fill each glass with about 2/3 cup margarita.
"During my time in Mexico working at the Four Seasons Resort Punta Mita, I lived in Bucerias, halfway between Puerta Vallarta and the hotel. My house was a small casita with beautiful mango groves in the backyard," recalls Chef James. "In the summer, I'd make margaritas with mangoes picked from the trees, fresh lime juice, tamarind, and some chile pequín. I had many of those margaritas, believe you me!"
Champagne mangoes are also called Ataulfo mangoes. Other varieties may be used but won't be as smooth. Use more mango nectar to compensate.