You will be able to use the sound system that is provided to play music during your event. There are three ways of using the speakers:
You simply need to turn on the TV and play music from YouTube or Spotify (the apps can be found in the TV menu). If having the TV screen turned on bothers you, you can go to the Display settings and select the "Energy saving" option to turn off the screen.
Connect your device to the Caucus Wi-Fi.
Launch Spotify on your phone and select a song.
Synchronize your phone to the TV by searching for nearby devices in the Spotify app (once you click on the "devices" icon, "Caucus TV" will appear in the list). You can also launch Youtube on your phone and cast to the TV.
The other option would be to use a laptop, by either connecting it to the TV via the HDMI cable that is provided, or by using the AirPlay feature if the laptop is a Mac. In both cases, you could display the laptop screen on the TV. The laptop would be the source and the sound would come out from the speakers.
In every scenario, you can use the TV remote to control the sound level.