DD how to find out about upgrade paths and firmware packages

Hello,

if the subforum is wrong please remove. 

We have 2 Data Domains 6300 with firmware 7.13.X. We would like to know what the latest firmware for these devices and the upgrade path is. They are used for backups and according to Veeam, 12.3. does only support up to DDOS 8.1, not 8.3. If I enter the serial of that device, I only get binaries for some versions 7.X but not for 7.13.X and neither for 8.1.X. How can I get the firmware packages and info on how to upgrade as well as upgrade paths (compatibility info in general)?

Best Regards