I sorted out some of the problem. I had set the H7600 device ID to 3, which I'd prefer, but it seems like VSigFile has no way of setting this parameter and only works with 1. So i switched the device ID to 1 and the H7600 responds to the Get DBase command. However, nothing happens on the PC side, and there is no MIDI signal flowing. I also connected the H7600 directly to my PC to make sure there was no MIDI chain problem. So it looks like the H7600 is both receiving commands from VSigfile and responding, but VSigFile receives nothing.
What do I need to do next?