ONIXEDIT Splitter is free software that divides one large ONIX files into several smaller files.
“ONIX files may be huge sometimes. Huge enough to get Out of Memory errors when trying to validate it or just open it using your best XML editor or best of all, ONIXEDIT! For that reason, we took the time to create a free easy tool that is able to read a ONIX file of any size and any type and to split it in smaller files. We called it ONIXEDIT Splitter and it is available for everyone. Just go to this page and download the installer:
http://www.onixedit.com/en/Software/Other/ONIXEDITSplitter.aspx
It is absolutely free and you don’t even need to be a registered user to get it.”