In reply to my own request: Xedit editor for the X3, X2, X5 etc. can still be registered. Please see the info. below from Joost Nieuwenhuijse Xedit's programmer:

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Hi Tim,

Yes you can still register at www.nstarsolutions.com. My email address has
changed to joost@newhouse.nl.
There will be no new development to Xedit, though.

Regards,
Joost
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I really would recommend checking this editor out if you own an 'X' series synth (I think it may also work with 'O' and 'i' series Korg's but I'm not sure.