I found a way to solve this, for those interested:
Code:
cd
mkdir -p .config/pulse
cat > default.pa <<EOF
.include /etc/pulse/default.pa
load-module module-switch-on-connect
EOF
After I wrote this configuration file, I turned off my computer, plugged the dongle in
and turned the computer on again, connected the speaker to the audio sink
When I played an audio file I could hear on the external speaker