Whisk together buttermilk, garlic powder, ½ tsp. each of the salt and pepper, and cayenne in large bowl. Add chicken; turn to coat. Cover and refrigerate for 20 minutes, or overnight.
In another large bowl, mix flour, cornstarch and remaining salt and pepper. Remove chicken from buttermilk mixture, letting excess drip off. Dredge chicken in flour mixture, shaking off excess. Place chicken on plate and set aside. In small bowl, mix barbecue sauce and maple syrup. Set aside.
Pour oil into large, deep cast-iron skillet or heavy saucepan to depth of 1’’. Set on medium heat until temperature of oil reaches 350°F. Fry chicken, 2 pieces at a time, turning often, until deep golden brown and crispy, 12 to 14 minutes. Remove chicken from oil to check that a meat thermometer inserted into thickest part reads 165°F. Place fried chicken on rack set on baking sheet or paper-lined platter to drain and place in oven on keep warm until you are finished cooking all the chicken. Brush barbecue sauce mixture over hot chicken.
Prepare waffles according to package directions. Place chicken on waffles and serve with leftover barbecue sauce mixture for dipping and extra maple syrup to drizzle.