You need to simulate a DAQ card capable of controlling an SCXI chassis. Ideally you'd pick the one you plan to use in your real system, but if not, just pick any multi-channel device with analog and digital input (I happen to have a PCI-6220 simulated already, and that seems to be valid). Once you have that device simulated you'll be able to choose it as the Chassis Communicator, and from there you can proceed to configure your SCXI modules. In your real system, this is the card to which you connect the cable from the SCXI chassis.
Again, as I wrote before, the SCXI chassis and the modules in it are not data acquisition devices, they are multiplexers and signal conditioners. You need to simulate a data acquisition device that will control the chassis and handle the actual acquisition, so that you match the way it would be set up with real hardware.
