An adapter will tune to exactly 1 multiplexer (mux) on the satellite position (or antenna) that it is connected to.
Each mux transmits many services that are multiplexed on the frequency.
If you have 2 adapters, each with the same network, the following happens when you record/view a service:
a. the active (currently tuned) muxes are checked to see if they contain the service you are looking for
b. if the service is part of an active mux, the use count of the mux is increased and the service is taken from the active adapter
c. if the service is not in an active mux, a free adapter is located and tuned to the mux that holds the service
d. if there is no free adapter -> failure
This applies to FTA services and softcams. If your adapters have hardware CAMs, receiving multiple services on one adapter may or may not work depending on your hardware.