If you buy a TV with Discover, AE, and many credit cards, you will get the 2nd year warranty for free anyway. I am not sure if you can get the third year on this deal if you pay with AE.
Use AX if you have it and the card has the benefit. They will give you an additional year on top of the 2nd year. Master Card's extended warranty version requires you to get a written price quote on how much it would clost to fix it. Just try to find someone who will do that for a TV....