<cfprocessingdirective> is irrelevant here, as it only relates to the source code of the file being compiled, not any data being processed.
<meta> tags are browser instructions, and as you're specifically telling the browser not to deal with this response, that's not going to help either. Try setting the encoding as an HTTP header (so with <cfheader> rather than with a meta tag.
That said, if you want an XLS file, simply sending text and saying "it's XLS" is not a good approach. Use CF's XLS-creation functions or POI to crate an actual XLS file.
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Adam