I had a similar problem once with a SXW file. You can still try one thing:
Rename your "xxxx.sxc" to "xxxx.zip" and try to extract the XML files. If that works, you can either compress them back to a ZIP and rename that to SXC or extract files from another SXC the same way and then swap files.
--
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"Er, five."
"Wrong! You see?"
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