i'll try to explain this as simple as possible,
on your hd is a directory called
emulators and evox (and maybe avalaunch) is set up to check in that directory,
so what you wanna do is make a new dir inside the
emulators dir and call it whatever you want,
like if you want to install a.. snes emulator? call it snes or xsnes9x or superdupersnesemu, it doesnt matter.
then unzip the emulator you downloaded from xbins and copy whatever was in the zip into that dir.
or just unzip the zip in a dir called snes and transfer that directory into your emulator dir.
then reboot and evox and avalaunch should show the emulator right away in the emulator section of the dash.