Sounds as if you are getting an error which is preventing the download. If you don't have the MIDI return connected you don't see it, which adds to the confusion.
My guess is that the error is caused by a version difference between the sigfiles and the unit. Try downloading the modules database from the unit (again if necessary). This should mean that vsig and the H8000 are in step, and any sigfiles you have saved in the past will show the errors is you try and load them into vsig.
Probably what has happened is that in the latest software one or more modules has had an extra parameter added or removed, which is causing your sigfiles to be out of step.