Hardware recommendation for striping an existing RAID Z2

[JJT211]

Here's my current hardware:

FreeNAS Stable train 11.2u3​

Supermicro X10SDV-4C-TLN2F w/ Intel Xeon D-1521​

64GB (2x32GB) Samsung DDR4 2133MHZ ECC RDIMM​

16GB m.2 SSD as boot​

RAID Z2 (6x4TB) WD Red NAS HD​

SeaSonic S12G-450 450W ATX12V / EPS12V 80 PLUS GOLD​

Fractal Design Node 304 Black Aluminum / Steel Mini-ITX​

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My current Mobo only has 6 SATA ports, but ive read I can install a SAS card to get more SATA ports. I'd obviously need a new chassis and probably a larger PSU, but I have no idea where to start. Any suggestions?