Do you intend on using HBA cards to run more drives on your unraid systems?
If you're using Unraid, you don't need all that (since the software is doing the raid for you)... You just need a bunch of disks (JBOD) hooked up to your motherboard.
HBA or host bus adapter, basically creates additional buses and gives access to cpu over pcie, it basically just converts pcie lanes to another component in this case raid controller cards. Crossflashing to IT mode (LSI by design) is used to allow different funcionality using the same chipset, in the case of NAS, it's to provide a true JBOD i.e. direct access to drives via the bus, rather than emulating it behind a RAID software.
PCIe 2 has 500 MB/s bandwidth per lane, so an x8 card(LSI HBAs tend to be x8) would have 250 MB/s available for each of 16 connected drives. A 16i card seems generally more expensive than 2 8i cards(or 8i plus expanded) but would save you a PCIe slot.
Any LSI HBA card in IT mode should work fine.
Most branded cards like Fujitsu, HP, Dell etc all start life off as an LSI card. That's why many (not all) can be flashed into "IT mode".
In this section, we will list the cards that our technical department have verified and tested to have been flashed into IT mode and ready for your UnRaid applications.