Few of the third party apps like soundflower and boom used to provide a master volume control for multiple audio output on OSX (aka combining USB audio output and 3.5mm output etc). None of the mentioned apps work anymore, say soundflower app cannot be loaded and boom 2 has a volume control but will not change the volume of multiple output devices. Is there someway on 10.11 to control the master volume of multiple audio output?
AudioMate gives you control over individual devices on menubar but it cannot change a master volume control for multiple audio output. Soundflower has one flaw that all your device must have the same output or it will not run - for example all of them set to 48K Hz 2ch-16bit. If you have a 4ch USB and a 2ch 3.5cm you will need to change your 4ch USB to 2ch, likewise on bit rate and frequency.