Heres a question that has probably been asked before, but I cant find the answer i'm looking for.... I have a old Dish Network 500 dish connected to a sw21 switch for sattelites 110 & 119 to a Dp model 510 that works great. I'm trying to connect a model 3900 (legacy?) receiver to this dish. What is the switch I need to use this dish 500 with these two different types of receivers?