succes
running under Proxmox
downloaded the 5592.1 iso from http://xpenology.me/downloads/ and uploaded it to proxmox
shutdown the virtual synology
replaced the 5565.2 iso in the virt CD player with the 5592.1 iso
rebooted the virt synology
the update to 5592 which is offered now works (unlike with the 5565.2 iso)
after reboot the virt synology finds 5592 patch 2
installed patch 2
after the auto reboot all works fine
Total elapsed time apx. 3 minutes
I'm a happy camper, thanks for another excellent piece of work folks!