A couple of notes about exporting to CSV.  Yes you will get any and all header info for each row (make a special report with out the header info, if you are using csv, you don't want that info anyway).  I do not know how you are exporting (to a file, application, etc.), if export to an application, then it will default to using a spreadsheet program to opening the file.  Also if you double click on a csv file it will normally default to using a spreadsheet application.  As far as the sub-report, I do not know.  I have never exported to csv when I had a subreport.