Off topic for Kronos, but I'm pitching in:
I actually still own my old Korg X3 (only difference is the number of keys, afaik), though it lives in our familiy's cabin, not at home, and it has been a few years since I last turned it on
I couldn't find the patch list for X2, but there is no piano named "X2 Piano" nor "X3 Piano" in the default patch list for the X3, nor do I remember ever seeing one. So I'm not sure this one is standard. So keep in mind that if you do a factory reset, chances are you're not going to get that particular piano sound back.
However, there is a pretty decent, though perhaps a bit on the soft side, piano in the GM bank, at GM-01 (the very first one).
And if you do a factory reset, you should have the "Piano 16'" in position A-01, and that one is a bit brighter than the GM, and was the one I usually used.
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Barring that, is there a floppy disk in it? Mine still has an ancient 3.5'' floppy that stores some .MID and .PCG files. The .PCG files, like on many Korg instruments contains "Program, Combi & Global" configuration. So if the previous owner backed up his sounds, you might find the sound again if you load the backup .PCG from the disk.
Though, again, keep in mind if you start messing with loading stuff from disk, that you'll at that point also overwrite the internal memory, and might end up ruining even more stuff...
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Good luck, it is a fun instrument that I have very fond memories of
