I use wet sanding and water to get the brushed look. Start smoothing the panel with some 80 grit on a DA, then move on to wet sanding with a sanding block and 220, 400, and progressively finer grit til you get the finish you want. The wet sanding has to be done in one direction to obtain a smooth and even brushed aluminum appearance. Time consuming, but worth it if that's the look you want!