You could go ahead and set up keyboard shortcuts in XFCE, so will not't have to do it manually each time. Here is what I did to change the headphone's volume. BTW change 'Headphone' to 'Speaker' to adjust the speakers
1. Applications Menu -> Settings -> Keyboard -> Applications and Shorcuts
2. Click add
3. Enter the shortcut, mine is
- shift - F8 for mute then enter $this->bbcode_second_pass_code('', 'amixer set Headphone 0')
- shift - F9 for volume down then enter $this->bbcode_second_pass_code('', 'amixer set Headphone 1%-')
- shift - F10 for volume up then enter $this->bbcode_second_pass_code('', 'amixer set Headphone 1%+')
Good luck
-Daniel