Focusrite Scarlet functions as my headphone amp, alt route to speakers and speaker stand.

I recently purchased a Focusrite Scarlet 6i6 but quickly ran into problems with Cubase 8 and OS X 10.11.5; the device worked with all other audio apps which made Cubase's VST system the culprit. For whatever reason, getting my Scarlet 6i6 to work required creating an aggregate device which still mystifies me. Aggregate devices in OS X allow you to combine multiple audio I/O sources into one virtual device for use in applications, regardless if the application in question has support for things like multiple audio I/Os or even something mundane like audio input from device A and playback on the device.

Step 1: In Audio Midi Setup, create an aggregated device

Step 2: Select the Focusrite, no other inputs/outputs are needed

Step 3: In Cubase, under devices, select Device Setup and set your device to the newly created aggregate device

Confirm all the ports are enabled and labeled in a sensible fashion

Under devices, select VST Connections and set the output to the monitor output

Under inputs in the VST connections, create any necessary buses needed for input and/or assign the ports as needed.