I just purchased a 921 and found out that you have to have 2 satellite connections to make it work. I only have 2 cable runs that go up to the dish. I also have a tv antenna. Radio shack claims that their diplerxer will split a satellite signal into tv and satellite. I want to split it and put the antenna splitoff into the back of the 921 antenna jack and the other into the satellite jack. The second cable run already goes from the dish to the appropriate jack. Dish says the diplexer will not work, radio shack says it will. Will it work and will it split HD signals appropriately. Can anyone out their help?