As the CPU of the old NAS was really a limit to many things - a NAS found a new home - using a 2.2Ghz Xeon CPU, 16GB Ram, and the storage has been expanded to 8 usable TB (that can be expanded to 12. Currently Raid 5 + 1 with 4 disks).
Added a 120GB SSD drive for the OS, and a PCIe eSATA Card to attache the external monthly backup drive. This new NAS is based on a HP Microserver gen8.
The only bad thing about this is that they use ILO internally (As a kind of BIOS replacement), and it is not easily accessible from within the system. And if using HP's tools, these cause the logs (because of an ACPI issue) to fill up pretty fast, and 50% CPU load for nothing. Hence - native snmpd-only for Monitoring. They should provide a classic ACPI monitoring access capability. The big advantage is that one can replace the mainboard with one other one, and add a Raid controller with Micro S-ATA for 4 to 6 disks - and that could take care of most issue !

Luck in timing... Once the old NAS was shut down, at the next power up, 2 drives did not come back up... Apparently, drives are not meant to last long anymore.