Master volume control for multiple audio output OSX
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.