Thanks for letting me know so quickly. I will install and configure these emulators outside of Retropie using sudo apt-get install.
I will keep tracking this in case they may be ported to the XU4 in the future.
@r34per actually I lied to you sorta. I almost forgot that RetroPie isn't strictly for the raspberry pi. You can also install it on x86 (Ubuntu) which you can install on a virtual machine. There are just some slightly different packages due to the diff platforms.