How can I send my computer's audio to multiple outputs? I'm sending my system's audio to Soundflower, but I want to send it to my headphones at the same time. Is there any way I can achieve this?
Open Audio MIDI Setup from Applications > Utilities.
Click the + button in the bottom left corner and select "Create Multi-Output Device".
Check “Built-In Output” (this may already be checked) and the Soundflower output of your choice.
Right-click (or control-click) the device you just created and select “Use this device for sound output”.