Quick note. I did manage to get my Voyager updated. I did use MidiOX, and the settings suggested above. (Thanks for posting them, Frank!!!!

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HOWEVER - it was still a painful process.
Basically, the Voyager ignored the SysEx dumps. I tried switching cables, rebooting the computer, trying Cakewalk, jiggling the MIDI connector, etc. Nothing worked. Finally, I tried sending the original System ROM image back to the Voyager. At that point, it seemed to "wake up", and listen to SysEx messages. Sent the 1.5 OS, 1.2 Boot, and Preset Files (in that order) and everything works great.
I think the key thing here is, if you're upgrading the 1.0 OS, make sure you're not in a hurry, and can take the time to do it properly. Also, use your favorite MIDI program to make backups of your System ROMs, Boot ROMs, and presets before you start the upgrade procedure. I made two each, then compared the dumps against each other, just to be sure!
It seems to go smoothly enough once you get it started, but sometimes getting it started can be tricky.
Cheers,
Paul