I think it should be possible to use some sort of "splitter" to connect the two tuners to the same DVB-S outlet.
No, not possible as the LNB (bit that sticks out the front of the dish on the arm) is powered by the device attached to it (in this case a DVB-S PC card but could be a set top box etc.) therefore each DVB-S input requires a seperate feed from the dish hence you have dual / quad / oct (2 / 4 / 8) output LNB's.
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