From what I understood by now ... xfce4-mixer is just a more stylish looking version of the alsa mixer command line mixer. It shows me too many things I dont care about; and it doesnt allow me to control the things I have to control. I understand that there are different usage patterns; but at least mine is a nightmare with that mixer: - i am regularly switching between single usage of my thinkpad ... or having it docked - i am using several different headsets (but just one at a time) So these are the things I need (and that are COMPLETELY missing with the xfce mixer): - the ability to setup a "profile" for audio devices - a SIMPLE interface that shows all available sources / sinks and allows me to make a selection (like gnome sound preferences). Or better, KDE style ... where the system remembers the order that you select for your devices ... so that when I unplug and replug a headset ... you dont have to go in and AGAIN tell the computer that yes, the USB headset is now the default again. - the ability to select the master channel ... so, when the USB headset is plugged, I can tell the system that its volume keys should be used to control its own volume; and not the volume of the Laptop-internal sound. Obviously this is would be a lot to do - but please consider reworking your mixer application.
xfce4-mixer is an interface to mixer controls provided by GStreamer. In the past this has served us well. However, with PulseAudio being around there has been a shift from configuring hardware controls to configuring audio streams. There are a couple of applications that come with PulseAudio (pavumeter, pavucontrol etc.) that might already support the things you want. Due to a lack of free time at my end, a complete rewrite is not planned at the moment. Maybe later.
Thanks for the update. Unfortunately the pulse controls are not sufficient; especially "setting the master channel" ... I have not found any solution to do that based on xfce.