In a large bowl, combine the first 7 ingredients. Crumble beef and sausage over mixture and mix lightly but thoroughly. Shape into 1/2-in. balls.
In a Dutch oven, brown meatballs in small batches; drain. Add the broth and pepper; bring to a boil. Reduce heat; simmer, uncovered, for 10 minutes. Stir in chicken and pasta; cook 5-7 minutes longer or until pasta is tender. Stir in spinach; cook until wilted. Sprinkle with shredded Parmesan cheese if desired.