grub.efi is irrelevant, you don't need it.
Have you updated firmware on your board as per the instructions in Getting Started Guide? Outdated firmware is the most frequent reason of not being able to boot from the SD card.
Thanks--that must have been it. I hadn't updated the firmware again after I reinstalled the IDE, and I also formatted the SD cards again and reloaded everything. I've got it going in Linux and now I'm hoping to have sucess with the Mac too.