If the N40L is still chugging along nicely, and the issue here is just it's inability to handle the compute side due to the antiquated Neo CPU etc. then put a generic uSFF in front of it to run services and let the N40L handle storage. 7thor ideally 8th gen onwards is still cheap and the real world power usage on your average uSFF of that vintage is low at idle and quicker to complete tasks when required. You could even go with one of the Lenovo's, add a PCI HBA with external SAS and convert the N40L to a DAS by going direct to the backplane, though the maths on that may not add up if buying new bits.