Do you have a ok backup, or will you have to produce a new and fresher backup from shell and then use this for the restore ? (That will also have to be done from shell as the backup will be different from the ordinary workstation based backup.)
I did this a few days ago a number of times for training purposes.
There is an issue if you want to make an upgrade to 6.0 at the same time. The directory structure of the 5.6 oand the 6.0 have changed a bit arount the area of the ibays and the primary directory, so if you just make an shell based restore, file for file and directory for directory, it will be a few problems about this (I ended up with a double set of primary directories and some other problems related to this.)
Backing up and restoring datas from and to v 5.6 worked rather ok using an extra hd, shell access and rsync. (It's rather easy to make the backup, but you have to be rather accurate doing the restore. If not specifying the datas right and precisely the rsync restore could quite easy crash the new installation. Anyhow you will still have the backup so you can make a new try.)
The procedure would eventually be something like this:
1. Install an mount an extra backup HD.
2. Miror over all central datas from the orginal HD to the backup hd using rsync.
3. Make a fresh new 5.6 installation.
4. restore bach the datas from the backup hd to the fresh installation using rsync.