13 feet is very narrow. There isn't room for enough air around the speakers. Consider turning listening area 90 degrees and put speakers along one end of the longer wall.
Not sure subs are the answer either in this very small compromised space.
I would take the electronics out of the cupboard and put on conventional racks. Move the cupboard to the other end of the room away from the sound action. Use the emptied shelves for more LPs!!