Just like you can damage your speakers by turning the volume too high with the normal volume knob, you can damage them by turning either of these volume knobs too high.
Turning up +15 dB is a lot. http://www.taringa.net/posts/info/5804731/Niccolo-paganini-el-violinista-del-diablo.html
Turning up +15 dB is a lot. http://goo.gl/3f2AUh