Hi
Midi input on the VS100(5pin connector): If you're using an external midi keyboard you can enter notes or play the instruments provided by you DAW.
Control (VS-100) is the possibility to control your track ( pan , vst, channel e.o)
When sonar was running for the first time was a message : do you have a midi controller that you want to use to control track/bus and plug in parameters ? When forgotten you have to execute the (options/midi devices) command to open the midi devices dialog box
and select both input and output for midi vs100 and control vs 100.
For sonar x3 maybe you have to look in references.