I picked up some older Supermicro machines from eBay (GREAT way to get some real server hardware, btw), but they have a VERY old IPMI firmware and no way to upgrade to a more modern version.
They can’t do standard virtual media — you have to specify a SMB share with an ISO on it to mount. Once you do that, you have to make it bootable in the BIOS and move it up the boot order.
I wasted about an hour trying to figure out why I couldn’t enable the device “PepperC Virtual Disc” in the boot order — the answer is, you have to use the ‘x’ key to remove unused devices from the 8 available boot slots, then you can select the PepperC device and use the ‘x’ key to enable it, and then you can move it up/down the boot order with the +/- keys.
Hopefully this saves someone else some grief, I was losing my mind trying to figure out the problem.