Surely I am missing something, can you explain what? If we shoot a gun while travelling on a train, the speed of the bullet is its usual speed plus the speed of the train vt, because the bullet inside is already travelling at vt. If we produce an EMR on the train (or on the earth in the case of MMX) the "bullet" is created on the spot and has no previous speed. So, why should the speed of light vary in any frame of reference? why look for the aether, why thw MMX? the speed of light depends only on properties of the medium and not on the speed of the emitter or the receiver.