Hi, I would say paint the inset walls a lighter colour that coordinates with the stone to make the stone "pop". Is your ceiling the same colour as the walls right now?

Hang something new above the built-ins (not sure of the rest of the room and your style) but hang it LOWER than what you have going on with the mirrors. If possible, I would recommend incorporating sconces or a picture light above the art work to brighten up the space. If not possible, lamps on the built-ins. I would keep the tops quite clear: a couple of large objects, baskets, etc.

We painted the ceilings white a couple weeks ago and are going to paint the inset walls a grey color to go with the rock. Thank you so much for the ideas!