On my px5s the volume of some stage settings seems to drop after a couple of hours. Not abruptly, but let's say I have the keyboard volume at "12 o'clock" when I start, and after maybe two hours I have to turn the know to "3 o'clock" to achieve the same out volume from my amplifier. And that without having touched the amp volume at all. After a restart of the px5s the volume goes back to normal again.