Hello,
I wasn't sure if I should start my own topic or not, but I'm having almost exactly the same problem. I've unpacked the data.xp3 file and I've figured out that the files are in ASCII encrypted with some sort of XOR cypher, but I can't for the life of me figure out how to repack a patch.xp3 so that it will work without the ASCII/Unicode error. Even just repacking the encrypted files gives the error (though I'm not surprised by that since I assume they used the built in encryption feature of the KiriKiri packer).
I know it's rude to drop in and raise this old thread, but I'm at my wit's end and would really appreciate if somebody could point me in the right direction. Thanks!