digital input using NI-DAQ USB-6501

I am wanting to take digital input using a NI-DAQ USB-6501 card into Superlab, on an OSX workstation. I see options under Event->Stimulus->Digital Output to select the card and I can set an entire port to input, but how do you get the signal in as a response to Superlab?

SuperLab supports output only on the Ni-DAQ card.