That is correct, but please pay attention to the fact that the engine doesn't support segment prefixes, such as:
ES:
so what you need to do is first move es into ds (which is where [0000] will access) and then do whatever you want. For example:
push es
pop ds
mov [0000], dx
Read my post please. The "es:" part is not supported by the game engine. As I said, you should do something like (because [0000] accesses ds by default):
push es
pop ds
mov [0000], dx