Storage server - Swapping SAS HBA card for a different model

You can configure a set of single disk RAID0 LUNs. Assuming you'll turn RAID controller cache OFF it should be acceptable equivalent of a pass-thru mode.

You can just use a standard LSI/Avago SAS HBA for this purpose. That's all that's necessary.

Since this is an old server... 11 years old, you should see a controller that is period-correct. I'd recommend a used LSI 9211-8i.

No drivers are needed; these are standard MPT Fusion kernel modules. You will need to figure out what to do with the operating system, though. I don't recommend ZFS for the OS drives. So you may need software RAID for that.