I discover that if i disable clear stereo and dsse (which produces artifacts on low frequency bass e.g. on infected mushroom's never ever land track), my nw-a808 don't skips when playing aac files. Also i must say that i found the skipping problem occurred rarely, on specific aac tracks and at the same track's position. Turning those options off the skipping problem disappears. Absolutely a firmware bug. Anyway, I'm happy now and i also like the sound of my 808 better with those options turned off. Now i must found which one of those two options causes this problem.