you have to wire it up like shown here
And yes, you need the audio. Talking of which. USB Audio is not good enough.
Maybe AudioInjector is shipping to Brazil.
There is a new HighQualitiy one coming up in a couple of months as well.
Please read this
http://wiki.zynthian.org/index.php/Command_Line_User_Guide
Section “Stopping/Starting the Zynthian UIStopping/Starting the Zynthian UI”
Now you see the reason for the error screen.