I get this warning message( Your feed appears to be encoded as “UTF-8”, but your server is reporting “US-ASCII” ) when I try to validate my xml under http://validator.w3.org/feed/check.cgi?url=http%3A%2F%2Fwww.domain.com%2Frss.xml
You should be able to set the charset in .htaccess. This should work:
# AddCharset UTF-8 .xml