Sir N,
I believe that your board have 3 output ports with 8 bits each, but this should not be a problem at all. If you select to have a 24 bit port and select the digital channel 0, the VI will configure ports 0,1 and 2 to create the 24 bit port. I would give the example a try just the way it is, I believe it should work just fine.
Gazoo!