Converting Office files in Enterprise to newer version w/o loosing history

OK Whos going to save my butt. Heres the deal. Our server has lots-o-files in .xls and .doc format. There is versions and revisions tied to these legacy files. Users want so save into the newer .xlsx or .docx format, while maintinging the history of the file. I was able to use convert inside Word to do a .doc to .docx file, but Excel is giving me grief. Is this the correct way

check out file

click convert inside Word

Save back into same path on server as .docx

check in

.doc file is replaced by .docx file and maintains versions and history.

Thanks

Scott