I use the Sanus posts from the Euro racks and make the shelves out of 3/4 inch oak-faced plywood. Shelf edges are covered with oak tape which is applied with a clothes iron. The resulting shelf looks better than anything you can buy ready-made and easily holds my Alpha 89 amp. For stability, the bottom of the posts are bolted to 3/4' pieces of solid oak that are just wider than the diameter of the posts and the length is about the same as the shelf depth. Suitable bolts threaded to mate with the posts are available at Lowes in the Hardware dept. The Sanus posts come in various heights - 5", 8", 10" and maybe others. They can be hard to find, but they're out there.
73, K8AC