For what it's worth: I had a MIDISport 8×8 several years ago. It did not handle System Exclusive messages correctly. I encountered this problem while using it with SoundDiver, a PC program for editing patches in MIDI synthesizers. I had problems with several different synthesizers while using this program. Eventually I tried using a different MIDI interface and the problems went away.
I am sure that Vsig uses System Exclusive messages to communicate with the Eventide hardware. As someone already suggested, your best bet may be to use a different MIDI interface or an RS-232 connection to your computer.