Ok, let me reply to myself in case anyone else sees this.
Excellent introductory article centred around Midi and Garage Band - MacJams.com - Article: MIDI Basics for Apple GarageBand Users
Now for a simpler question. I have a Midi - USB cable. Can I go direct from the Acuna into my Mac or do I need to go via an interface box of some description?
I can't get Garage band to play a note via Midi - USB. It sees the input and in Audio Midi set up it sees the device as well as in GB preferences. It just won't play any notes. Works ok direct in from USB to USB though.
Any guidance? Thanks