About time your on this forum abu as your on most others and mod on most of them,One of the best around you are sir.Enigma2 will select the tuner appropriate for the service.
Tuner slots are on the circuit boards
Tuner cards go in the slots on the circuit board.
One twin tuner tuner card will go in one tuner slot. Result = two sat tuners.
Two single tuner cards will go in two tuner slots. Result = two sat tuners.
Best to buy a twin tuner card as they are generally cheaper than two singles and you have option of using another tuner card at a later stage.