I have been doing some research on those cards and yeah there are some places you can get them fairly cheap. The one thing I have been a bit confused about though is it seems like you can just configure drive passthrough directly in Proxmox to virtualized TrueNAS, and from what I understand that is similar/the same to using a physical HBA card in a PCIe slot. I suspect there is something I am still not understanding with that though, so more research for me, haha! Thanks for the advice on the cables :)