Using H710 and H810 together (UEFI0116 error)

Hello,

I have an R430 with an H710 adapter. I use Windows in UEFI boot and all works fine.

I intended to add an MD1200 via an H810 PCI card but when I insert the card I get an UEFI0116 error and a boot loop.

Googling suggests that I needed to remove the card, boot in BIOS mode and this works (the error disappears), but then I cannot boot the OS from the drives on the H710 adapter.

My intention was to use the H710 with the onboard drives to run the OS and have the main storage on the H810 and MD1200.

Is that configuration not possible?

If it is possible, what am I doing wrong here?

I guess if not I will need to just run the OS from the MD1200 via its own virtual disk and RAID and then have the main storage on a separate VD and RAID.

Thanks in advance.