Multimedia Keys
We learned that multimedia keys are available by using showkey. To use it, one has to go to a text terminal, start showkey and press the buttons in question.
The shown keycodes should be placed in ~/.Xmodmap
keycode 234 = XF86Back
keycode 233 = XF86Forwardpre
keycode 144 = XF86AudioPrev
keycode 164 = XF86AudioStop
keycode 162 = XF86AudioPlay
keycode 153 = XF86AudioNext
keycode 160 = XF86AudioMute
keycode 174 = XF86AudioLowerVolume
keycode 176 = XF86AudioRaiseVolume