1. In large skillet, heat 2 tablespoons oil over medium-high heat. Add onion and fennel; saute 7 minutes, until tender. Add mushrooms and garlic; saute 6 minutes. Add paprika, oregano, sage, 1/2 teaspoon salt and 1/2 teaspoon pepper; saute 2 minutes. Cool to room temperature.
2. In bowl, combine 1/2 cup bread crumbs and milk; soak until softened.
3. Transfer mushroom mixture to food processor. Process until coarsely chopped. Add to soaked crumbs in bowl, along with chicken, veal, eggs, the 1/3 cup crumbs and the remaining salt and pepper; mix to combine. With wet hands, form into meatballs, using about 1/4 cup per meatball (you should have about 21 large meatballs).
4. In large skillet, heat remaining 2 tablespoons oil over medium-high heat. Working in 2 batches, add meatballs; saute until browned, 6 to 7 minutes per batch. Remove the meatballs with slotted spoon to a large platter.Sauce and Spaghetti:
5. In large, deep, heavy saucepot, heat oil over medium heat. Add onion and fennel; saute 7 minutes or until softened. Add plum tomatoes, diced tomatoes, garlic, red wine, sugar, salt, oregano, sage and pepper, breaking up tomatoes with wooden spoon. Simmer, uncovered, over medium-high heat 10 minutes (you should have about 9 cups sauce).
6. Carefully add meatballs to sauce, trying to submerge them, if possible. Cover and simmer for 15 minutes or until instant-read meat thermometer inserted into center of meatballs registers 160 degrees F.
7. Meanwhile, cook perciatelli following package directions. Drain pasta; transfer to large serving dish. Top with meatballs and sauce. Makes 8 servings.