Hi Paul,
Sorry for the delay. I just wanted to let you know that your advice got me there! I was in fact using a mix of BOOTAA64.EFI/grubaa64.efi from different urls. I got lazy, and downloaded them from different repos and didn't check to make sure I had matching versions. When I downloaded both the dvd iso and the netinst iso from the same location, and got the files I needed from them, it all started working.
Thanks for the pointers.
--Chris