I found a way* to dump 2 TX7's worth of DX7 sounds via MIDI as SYSEX onto a computer; Once this was accomplished, Yamaha's FM Converter page worked very easily and quickly, auto-downloading the banks as Montage .XL files into my (Mac) Downloads Folder. Then I dragged these library files that FM Converter had just created, onto the Montage's USB stick (which I moved over to the computer to load up.) Putting the USB stick back into the Montage, I easily loaded each TX7 bank into an empty Library Slot (I only had the Boesendorfer Library installed up to then, so there were 7 empty Library slots.)
And I'm having a great time tweaking and combining TX7 (and soon, DX5) sounds into Montage Performances.
I suspect that over the 30 years the sounds were sitting in TX7's, a few Parameters suffered data loss or slippage; plus, with 2 extra Operators (1+2) and more Algorithms, and a few new Montage FM Parameters, there's some work to be done. But I'll be posting a few soon. They really do sound as full as the TX7's sound to my ears in these modern times, and as responsive to velocity in nuanced ways that seem only possible via FM.
Bravo, Yamaha!

*(for months, I was stuck in old thinking, trying to figure out how to translate old Galaxy sound banks into SYSEX format, so that FM Converter could read them. But once I gave up on that old thinking, plugging in a standard 2 Midi-5pin to USB cable into the TX7's MIDI OUT, and the other end into the laptop, opening SysEx Librarian program on the Laptop, setting it to record, and then hitting Shift and then DUMP on the TX7 did the trick.)