1. Run: pactl list short sinks

2. Note the device name you want to use as default

3. Try to run: pactl set-default-sink

     This should work without giving you an error message.

4. Open the application "Startup Applications" (Should be preinstalled on Ubuntu)

5. Click on "Add"

6. Give your startup item a name

7. Copy your command from above into the command field:

     pactl set-default-sink 'Your-Device-Name'

8. Click on "Add".