Yep,I used to have the center just sitting on the stage angled upward towards the listeners, but it works much better now mounted on the wall. Besides you want a slight arc shape anyway from your left to center to right, so having the center set back slightly from the front of my m60's works perfect, the distance to my primary listening position is the same for all three.
The stage, if I recall, was built out of 2x8's. It is actually two stages, one 7ft long and the other about 8ft long to fit the width of my 15ft screen wall. I also used some 2x4's as cross members about every few feet fore extra support. The top plywood just sits on top and is wrapped with the same padding and carpet as in the rest of the room. This way I can get to my wiring easily for future additions. I also filled the void with thick rolls of paper backed insulation.
