1. Do first a backup of the configuration of your current Synology via Control Panel > Update & Restore menu > Configuration Backup tab > Back up configuration button
2. Move the disks to the new Synology, keeping the very same order (disk in bay n must go into the bay n of the new Synology).
3. Add a few other disks in the new Synology and create new Volumes
4. Boot the new Synology and wait for the beep.
5. Start the Synology Assistant, find your new Synology and click “Connect” on it.
6. Use the Migration mode, keeping all your files. NB.: you should download the latest DSM for your new Synology and use that local copy during the installation process instead of letting the installation process download that file itself.
7. Restore the Configuration backup on the new Synology
8. If you were using the web station and php, enable it. This settings was lost in my case: Control Panel > Web Services menu > Web Services tab > Enable Web Station option
9. Repair the packages one by one. Wait for each repair to be successful before repairing the next package otherwise you could be in troubles. Pay attention also that the behaviour of the UI can be weird when auto-refreshing after a repair. If clicking repair on a package, you see that the package repaired is not the one you clicked on (but one that was already repaired), close and reopen the Package Center. All my packages where successfully repaired (sometimes I had to skip one and retry later, IMO due to the dependencies…). Here are the packages I had to repair
   1. Audio Station. everything kept as-is, including the user-defined radio
      1. if music does not appear, go to Control Panel > Media Indexing and re-index the media files.
   2. Download Station: didn’t lose anything from its download queue
   3. Plex Media Server. I simply had to reenter my credentials which were expired
   4. DNS Server: all settings/zones still defined. Access to all services from intranet and internet working fine
   5. Maria DB: nothing lost. In particular my Worpress blog.
   6. Media Server: ok
   7. Video Station: all video and metadata accessible
   8. Photo Station: all albums still there and ok
   9. Python 3: I had to retry the repair but works fine
   10. Java Manager: ok (used to install Java 7)
   11. Surveillance Station: Licenses, settings, camera, recordings are all kept
   12. Time Backup: I had to retry the repair but backup tasks are ok, as wel as the timeline itself.
   13. Node.js
10. Other Packages:
    1. My Custom packages were still there: iPKGui, AcpiOnLan, Mods (My Own Dsm Shorcuts), Unofficial Java Installer (Java 8)
    2. Custom Package Sources are still defined too
    3. Jdownloader was still installed and configured and I only had to restart it.
    4. Settings were lost for FileBot Node. After reconfiguring FileBot Node, it was not working (unable to access its onw port) I had to uninstall it and reinstall (including FileBot). Reconfigured settings were however not lost…
    5. WordPress was stopped. My blog was however well still accessible as I did reenable the Web Station
11. Synology’s DDNS Service
    1. DDNS Service being linked to the old Synology, I had to go to https://account.synology.com/fr-fr/overview and unlink my DDNS name
    2. Next, I went to  Control Panel > External Access and did Edit my provider (Synology) to re-enabled the DDNS and re-introduced my login/password.
    3. It took a few minutes before being again connected.
12. I finally moved a few Shared Folders to the new volumes by editing them via Control Panel > Shared Folder menu > Edit. I simply changed the location, picking the new Volume as a target. Attention, during the move, the Control Panel is not accessible anymore. If you need to access it, simply open a new browser 😉 (The only thing that cannot be done, is moving two Shared Folders simultaneously). Notice that the move can take ages as the new volume is probably still under validation (depends if you checked that option when you created the volume).

Et voilà.