Multiplayer option in MB STUDIO PRO plays the elements on different outputs of the sound card alternately. For example: having activated outputs 1-2 and 3-4 and activating the Multiplayer option the first element plays on output 1-2 and the next on 3-4 then again 1-2 and so on automatically and without user control. This configuration is tipically used in radio studios on 2 sliders of the external hardware mixer: during a speech operation, the slider of the element that is aired is lowered while the slider of the next element stay up so when clicking NEXT, the next element is already full volume.
The Multiplayer option is only available on MB STUDIO PRO and only if the card espose to MB STUDIO more than 1 output. Usually via ASIO all card outputs are instantly available, however as the first choice for stability is the Windows audio engine, it is good to try to enable all card output channels in the Windows audio configuration (not always possible but it's always good to check)
Let's see an example with the M-AUDIO DELTA card: select the M-AUDIO multichannel
go to adavanced and select a 4 channels profile:
Now you can run MB STUDIO and choose that device: the channels switch appears and you can enable the outputs you want:
To use Multiplayer, activate at least 2 outputs (you can still use up to 4 outputs if available in your card)