My memory doesn't serve me well enough to be certain, and I wouldn't swear to it, but I think that this program or something very similar to it may have also appeared on the Atari platform. Not sure at all if it ever made it to "PC".
I still have a ton of Atari based programs that I can use via the "Steem" virtual Atari emulator for PC. There is a DX7 patch edit program listed at Tim Conrardy's Atari midi website, but I have no idea whether it is similar to what you have. You could check it out if you wanted to at:
http://tamw.atari-users.net/timidi.htm The PLG150-DX plug in for the Motif and Other Yamaha synths has a similar editor. I know it works with a graphical interfacesuch as the one you describe. If I read correctly, it can also edit the patches on a DX-7. It was available with Yamaha XG works soft sequencer, and likely with the plug in itself as well, but you would have to do a search to see if a standalone version exists if you don't have XG works or another way to acess the plug in.
Regards,
AJ