If I create a multisession disc, can EMC8 be set up to automaticaly check which files on it have been updated and then set up to append the new versions?

Backup My PC found under the Home, applications tab can do this, but it's more of a backup program. All this means is that your files won't just be on the disc, they'll be in a backup format that will require you to use the application to extract/add files from/to the disc. What you're looking for is a differential backup.