Melt butter in heavy large saucepan over medium-high heat. Add beets, onions, celery, cabbage, and chiles; sauté until celery is soft, about 10 minutes. Add 5 cups broth and lime juice; bring to boil. Reduce heat to medium-low. Cover and simmer until vegetables are very tender, about 1 hour 15 minutes. Working in small batches, puree soup in blender until smooth. Return soup to pot; season to taste with salt and pepper. Add more broth until desired consistency is reached. Ladle soup into bowls and top with tortilla chips and sour cream.