To do this, you'll have to go back to Audio MIDI Setup and do it from there for each of the outputs. Select the 'Multi-Output Device' that's now there.Īn unfortunate side-effect of this, as 'The selected device has no output controls' eludes to, is that you now can't control the volume in the normal manner. Start 'System Preferences' → 'Sound' and click the 'Output' tab. Select the Multi-Output Device that has been added and in the right-hand pane, select both the 'Built-in Output' and your USB device.
Select the '+' in the bottom-left and select 'Create Multi-Output Device' In order to get this to work, you'll need to plug in the USB device, then do the following: Now this may not answer specifically what you're asking, but for interest, the only time I've had any success with simultaneous headphone and speaker output is when using a USB device, such as a headset or USB speakers.
There are several discussions around as to whether this is actually a limitation in the hardware or the software, but the end result always seems to be the same. As soon as you plug in the headphones into the 3.5mm jack, it replaces the internal speakers as the default output (and vice versa when you unplug them).
