@dereksanderson Firstly, the Raspberry Pi is an ARM based single board computer as opposed to a x86 intel based pc. You cannot therefore expect a linux based "image" that has been configured for a Raspberry Pi to boot on a pc. You will need to follow the documentation to achieve what you want...

https://github.com/RetroPie/RetroPie-Setup/wiki/Debian

Second thing to note regarding "a great image from MLPIXEL (a 32GB) which boots on Rasperry Pi ". If this has roms then it is illegal. You should check out point 5 of https://retropie.org.uk/forum/topic/3/read-this-first as indicated from @buzz as I was typing this very line.