Why sounds different the sound that I made on Dr Rex. when in preview from to track? Anybocy?

You will have to be more specific i am afraid. I have never had this problem. However when you go "to track", Reason loads the Rex file into the sequencer & assigns the events midi notes so there may be something happening (or not) in your sequencer. After you go "to track" check & see what is happening in your sequencer window to the Rex file.