Imagine the following scenario. You've got a MacBook running Logic Pro, an iBook G4 running NI Kontakt and one MIDI interface.
How can you use the single MIDI interface simultaneously for both computers?
Solution: Use the standard OS X Utility "Audio Midi Setup" and send MIDI through a network connection. In this case through the airport.
In my setup I connected the MIDI interface (Emagic MT4) to the MacBook that's running Logic Pro.
1. Open Audio Midi Setup on the MacBook. Go to Midi Devices and double click Network.
2. Create a session (MacBook) and activate it. Live Routings is patched so that the incoming Midi port (MT4 Port 1) is send to the Network (Network Macbook). Settings for Who may connect to me= Any computer.
3. On the other computer (iBook G4), open Audio Midi Setup, Midi devices and also double click Network. Create a new session (iBook G4) and activate it. In the directory window select the computer to which you want to connect (dvdborn) and click on the connect button. Both computers now share the same MIDI interface. In the black bar, horizontal red lines will show the latency between the 2 computers. I had a latency of 12 ms which is acceptable.
It's essential that the Audio Midi Setup utility is running on both computers. The connection won't work when you quit the application.
In my case all the incoming MIDI data on port 1 is being shared between both computers.
In Logic Pro you'll find an extra MIDI output port (Macbook). Everything that's being transmitted on this port will be sent to the iBook.
And just for the sake of it, here is a lousy video demonstrating the above mumbo jumbo in action. There's no sound on the video. Just me playing the EIII that's connected to the MIDI interface of the MacBook which in turn is controlling Kontakt on the iBook. Only the audio out and power connector are connected on the iBook. You'll notice the level meters moving in the upper right corner. That's a sign Kontakt is playing.