To make marinade: In a small bowl, combine 1/3 cup maple syrup, paprika, black pepper, salt, onion powder and thyme. Cut each rack of ribs into 4 pieces; place in a large nonreactive baking dish. Pour marinade over ribs and rub into both sides, distributing it as evenly as you can. Cover dish with plastic wrap and refrigerate at least 4 hours or as long as 8 hours.
For preliminary cooking: Heat oven to 350 degrees. Add about an inch of water to roaster or other large baking dish. Place a rack in the roaster, propping it up on balls of foil if necessary to raise it above the water. Stack the ribs on the rack; pour any liquid that has accumulated under the ribs into the roaster. Seal the roaster tightly and bake for 1 1/2 hours (see Note). Remove roaster from oven and set lid slightly ajar; let ribs rest for 30 to 40 minutes. while ribs are resting, prepare glaze.
To prepare glaze: Combine 3/4 cup maple syrup, apple juice, tomato paste, onion, mustard and chile-garlic sauce in small nonreactive saucepan. Heat to boiling, adjust heat so mixture boils gently, and cook, stirring occasionally, for about 20 minutes.
Once ribs have rested and glaze is ready, you can proceed directly to grilling or else refrigerate ribs, loosely covered, for up to 12 hours before grilling. Also cool and refrigerate glaze if you are going to wait more than an hour before grilling ribs.
To grill: Prepare grill with direct, medium-intensity fire. Place ribs on grate and cook until hot, turning frequently. Brush generous layer of glaze on the top side of the ribs. Cook for about 2 minutes, then turn ribs over and brush again with glaze. Continue cooking ribs, turning every few minutes and brushing with additional glaze, until ribs are crusty and browned in spots, 5 to 10 minutes.