You can't split the signal from the dish. You can get a dual head LNA and run one to your existing receiver and another to the other receiver.
OR you take the output of the receiver and split that. But that gets you the same channel on both systems.
I just had my basement finished and ready to set up a home theater system and tv. Whe they finished the basement they took an existing cable wire that was running to the second floor and split it to run to the basement. Originally I had direct tv and they said that this cannot be done. that each received needed a dedicated cable line from the dish. Is this the same with cable, and will the picture quality be hurt?