The pass through or loop through will limit your satellites and channels to what ever satellite and transponder the main receiver is on.
If you only have the two receivers then it all depends on what type(s) of LNB's you have on the dish and how many and what satellites your looking at.
If only one satellite then a dual output LNB could be used, this would supply both receivers and allow independent channel control at each receiver.
If two or more satellites (it would be nice to know how many your currently receiving) it again depends on the type and make of LNB's on your dish, then a switch may be needed, for two receivers a 4x4 switch would work better, this would allow for independent channel selection on each receiver.
What type of LNB(s) do you have on the dish now?