I think what dailo is looking for is a splitter on the off air antenna. If he hooks the RF output to the cable in his house then ALL of the TV's will be stuck watching the same channel.
What you need to do is get a satelliet grade spliter and split the coax before it reaches the voom box. Then take 1 piece to the Voom box and the other to the cable already existing in the house.
Or if the installer simply attaches to the existing run of cable coming into your house your problem is already solved. In that case you will effectively have off air and sat signals running to every jack in the house. If you plug a regular TV in it will be able to tune off air stuff. At a later date if you decide on more voom receivers just connect the cable to it and you're watching HD.
I am going to assume you are splitting the coax that comes into the house through multiple splitters. You need to make sure they are all satellite compatable. If the aren't you won't be able to get the sat signal through them. What would be best is one main splitter that way there is less loss.