I beleive you are corect and it is too old, I dont think any from this era are editable like the newer ones are. You can do some midi stuff with them but probable too old.
Not in ToneLib, but you can still use the official ZOOM Edit&Share editor, download it on the support page. ...SCRATCH THAT. The G1XNext apparently does not have any USB or MIDI external capability, so nothing to attach to. I mistook it for the the G2Nu, which can be edited with Edit&Share.
