Thera are only devices shown wich you normaly use with VISA. To show all your devices start the MAX. Select Software -> NI-VISA. In the window which is now displayed at the right side select General Settings and change the "PCI/PXI and FireWire Interfaces" setting to "Show all devices accessible to VISA". If you run the C# Example again you get listed all your devices.
But for example to use your PXI-6259 M-Series Card is much simpler to use the DAQmx. Have a look at the DAQ sample projects.