Tboooe,
No doubt, that nook is causing the "soundstaging" problem. You might want to try placing your speakers outside of the nook and see what happens. Had a friend who used to play in a band, and in one of the places they used to play, the stage was built into a nook (which he described as playing inside a box). Consequently when they played there and put the PA on the sides of the stage they would have problems with the sound being distributed throughout the room. They somewhat solved the problem by placing the PA offstage and to the front and the far sides of the nook, thus minimizing the effect that the nook was causing to the sound.