centos 6.8 with gnucash 2.4.15, export file is limited to 'xml' type, which is stated in documents.
this is a drastic problem in that 2.4.15 can not create files for merging into other files.
please consider this as a request to update current centos 6.8 package of gnucash 2.4.15 to a later version in 2.6.x releases.
look forward to reading announcement.
thank you.