Flavours ox Excel export?

I know that there is a bunch of several Excel-Formats, all sharing the same file-extension ".xls" and depending on the version (and/or even platform/OS) of Excel/Office.

I am using Excel-Exports for importing the data to FileMaker. However, FileMker (8.5) does not like the html/xml wrappers that PHPrunner generates. I once succeeded in generating a FileMaker-compatible file, but - without any obvious reason, except upgrading from PHP 4.4.8 to 5.2.5 and back down again - this does not work anymore. <img src='https://asprunner.com/forums/file.php?topicimage=1&fieldname=question&id=9116&image=1&table=forumtopics' class='bbc_emoticon' alt=':huh:' />

Is there an option to get back to the old format or to implement more than one Excel-Format as an export option?
tia, ppaul