The volume control part of pommed is implemented by mapping the volume buttons to the levels of one ALSA channel (ideally the master level) and the mute button to the on/off status of two channels (in the default config, Speakers and Headphones). On a MacbookPro8,1 with a mostly clean base Wheezy + task-lxde-desktop, either the "Master" channel has to be muted or all 3 of "Headphones", "Front Speaker" and "Surround Speaker" to completely disable sound output, neither of which appears to be possible according to the configuration file. In the meanwhile I remapped the headphone control to the woofer.