I still don't understand what I need to have a "proper" area51 setup.

I currently have the following in my ROMS directory...

folder: area51r3k -- contains: area51a.chd
folder: area51 -- contains: area51.chd
folder: area51a -- contains: area51a.chd
folder: area51mx -- contains: area51mx.chd
I do NOT have a folder for area51mxr3k or an area51mxr3k.chd

cmp332b says everything is ok but something still seems wrong to me. Have I got all the folders and CHDs correct?