I also don't think that Madara intends to have Sasuke fight Naruto simply to have Sasuke capture him. Madara made it seem important that Sasuke and Naruto fight, not so much that Sasuke capture Naruto. If it was merely a case of capturing Naruto, Madara has other options. I am certain that there is more to it than that. Sasuke and Naruto fighting must have some significance. I think it is interesting that Madara aquired the powers of Hashirama during their battle and now he intends to have Naruto and Sasuke clash, almost recreating that situation. Since the Valley of the End, a comparison has been drawn between Madara and Hashirama, and Sasuke and Naruto. My guess is that Madara intends to recreate some type of reaction during that fight and through their fight he will be able to obtain something. I don't know what specifically but I definitely think that their fight is for the purpose of Madara's gain and goes beyond simply aquiring the 9-tails.