Hi,
In my config I use one Media Type for each AutoChanger.
Each Autochanger it's linked to a set of clients (all of them for the same corp.) and each autochanger has its own restore device with autoselect=no.
Bacula try to use the device for restore with higher number of concurrent jobs.
You can check it in this whitepaper:
"To be able to restore a file concurrently with backups, the last Backup device should
have a large “Maximum Concurrent Jobs” setting, and the last device will be used
automatically for Restore."
Hope it helps.
Best Regards
J.