How to upgrade Emailxtender 4.6 to 4.8 to another hardware and sql version?

EMC should create a migration guide if one doesn't exist. I've performed migration in the past by copying all the .emx file to new server hardware running a fresh instance of EX. I then add the volumes from Lost and Found. This step recreates sql entries in the new db and rebuilds the fulltext index. You can then reconnect the journal mailboxes to the new machine. You can also update the EmailXtender custom recipient in the GAL with the new server address if you're running shortcuts in Exchange.