I guess they're not implemented for the 6g. Shouldn't be necessary to change them anyway.
Edit: Actually looking at the source, the 6G doesn't define HAVE_DISK_STORAGE, which means the storage related menu options aren't presented. Not sure if thats an oversight or if there is some reason.
Edit2: If you want to try, here is the current build (1fbdc28) with HAVE_DISK_STORAGE defined in the config file, so it should let you have those options back (untested so it may not work)
http://mit.edu/mgg6/www/rockbox.7z