That's nice, that it's not a JSL-bug :)

Have you tried a manual dump from the XP-30 using the generic driver?
If it doesn't work, I'll help you writing the library support, as usually that's the easiest part.

1. http://jsynthlib.wikispaces.com/synthDevice
2. http://jsynthlib.wikispaces.com/Step-by-step2
3. http://jsynthlib.wikispaces.com/synthPatchDriver

Of course we'll need some sysex info about the XP-30 but that's all described pretty well in the manual I downloaded.
Just a matter of a little searching and collaboration. While we/I write a driver for the XP-30, it would be a good occasion to extend the wiki with more examples/details, to make a better tool to use when writing a driver.

And there's also the XML Driver where you can describe your synth's SysEx in an .xml file to have library and editor support.
The XML Driver was written by Rib Rdb but there's no documentation written for it yet, only this:
http://jsynthlib.wikispaces.com/XMLguide