Prepare rice mixes according to package directions.
Meanwhile, melt butter in a large skillet over medium heat; add celery and onion. Sauté 10 minutes or until tender.
Combine water chestnuts, cooked rice, celery and onion, chicken, 3 cups cheese, and next 5 ingredients in a very large bowl.
Spoon mixture into a lightly greased 15" x 10" baking dish or a 4-quart baking dish. Top casserole with breadcrumbs. Bake, uncovered, at 350° for 35 minutes. Sprinkle with remaining 1 cup cheese and almonds; bake 5 more minutes.
Note: You can divide this casserole evenly between 2 (11" x 7") baking dishes. Bake as directed above, or freeze casserole up to 1 month. Remove from freezer, and let stand at room temperature 1 hour. Bake, covered, at 350° for 30 minutes. Uncover casserole, and bake 55 more minutes. Sprinkle with remaining 1 cup cheese and almonds; bake 5 more minutes.