I just updated a Space via MIDI on my Mac using the Eventide Update Utility, and there wasn't much too it. I connected an M-Audio Uno midi device to my Mac and connected the cables to the MIDI jacks on the Space. I rebooted the Space in update mode. (This might not have been necessary, but you should make sure it's not connected via USB, b/c it can't talk to USB and MIDI at once.) And then I launched the Eventide Update Utility, and it found the Space stompbox without my needing to tell it what port to use. And then I just proceeded to update as you usually would with the Eventide Update Utility.
