You mention you have 2 dishes outside, do you know what they are aimed at, same point in the sky or differnt? How many leads come off them?
Each dish will have an "LNB" at the centre of the dish, these can have one, 2, 3, 4 or more connectors. The more conenctors you use the more channels you can tune into if you have enough tuners.
Typical pc tuner cards will use one connector and lead. If you want to use watch more channels you use another tuner card and cable.
typical recent sky dishes will have a 'quad lnb' ie 4 avilable connectors, older ones probably just 2 with only one cabled up.