In a large resealable plastic bag, combine peaches, peach nectar, and peach schnapps. Seal bag, and marinate for 1 hour.
Remove peaches from marinade, reserving marinade. Grill peaches over medium-high heat (350-400 degrees) for 5 minutes per side. Slice peaches lengthwise; set aside.
Preheat oven to 350 degrees.
Place butter in a 13x9-inch baking dish. Place baking dish in oven until butter is melted.
In a medium bowl, combine biscuit mix, sugar, and half-and-half. Pour batter into baking dish over butter. Arrange peaches on top of batter. Do not stir peaches. Pour reserved marinade over top of peaches.
Bake for 55 to 60 minutes, or until lightly browned. Serve warm with ice cream.