Obj is a static mesh and it does not include any information regarding bone and animation while exporting. There are no useable x file exporter available for maya, I afraid. But you can use the exporter that comes with directX SDK.
There is another x file exporter available for maya provided by a game engine(I downloaded that but hv not used that yet), I don't remember the name, since I am not on my computer.
Everyone says that directX SDK has the best x file exporter. Srry, but I would not be able to tell about this anything. Bcos I don't use it either.
If you want you can try this.
Regards
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