Let me applaud you for selecting an LED source. I always hated replacing those stubby little halogen bulbs in my puck lights. They would get instantly hot and burn my fingers. First of all, I would see if the puck lights you have offer any accessories. If so, I would add a spread lens, along with a hexcel louver. A better solution would be to install linear LED strip lights along the top of each niche. The light source will be hidden from view and provide a more even illumination for your collection.