Hi !
We unfortunately haven't got any VCI-300 at MixVibes yet.
So we, for the moment, can't tell you how to make it work with MV !
By the way, you can try this utility (MidiOx :
http://www.midiox.com/) to monitor the MIDI messages sent by the VCI-300.
Let us know what MIDI messages are sent (if they are), by copy-pasting from MidiOx interface or making some screenshots, and many people here will be able to tell if these messages can be easily understood by MV or not !