Unable to use Audio Midi Setup to use two audio outputs I used to have an aggregate device where I would have my audio output coming out both my Bluetooth headphones and my built-in speaker. (Weird, I know. I used the setup to play along with musical recordings.) Suddenly one day it just stopped working, so I delete the aggregate device and tried to make a new one. But I'm unable to get the sound to come out of both devices.

The sound only comes out of whatever subdevice I have listed first. I've tried changing the clock source, the sample rate, and check-marking the drift correction. And it always just coming out of one device.
Use a Multi-output device, rather than an Aggregate device.