How do I switch to another audio output sink in XFCE?

After installing pavucontrol you have graphical access to several useful settings for pulseaudio including a choice for your output device. Choose the default output device in the Output Device tab:

A currently playing stream of a given application can also be moved to another device in the Playback tab from the dropdown menu next to Playback Stream on:

The pavucontrol answer is correct. However I encountered difficulties to use is out of the box. I had to type the following before using pavucontrol to use my bt headphone:

pactl load-module module-alsa-sink device=btheadset

You can control if this was successful by typing:

pactl list short sinks

Output should look similar to:

0 alsa_output.pci-0000_03_04.0.iec958-stereo module-alsa-card.c s16le 2ch 44100Hz SUSPENDED

2 alsa_output.btheadset module-alsa-sink.c s16le 2ch 44100Hz IDLE

I also have a short script to move sound from alsa/pulseaudio to bt that I called 'toBt.sh':

#!/bin/bash

OCHANNEL=`pactl list modules short | grep btheadset | cut -f 1`
for i in $OCHANNEL; do
        echo "altes module $i"
        pactl unload-module $i
done
CHANNEL=`pactl load-module module-alsa-sink device=btheadset`
echo "neues module $CHANNEL"
if [ $? -ne 0 ]; then
        echo "No bt connection"
        exit -1
fi
SINK=`pactl list sinks short | grep btheadset | cut -f 1`
INPUTS=`pactl list sink-inputs short | cut -f 1`
for i in $INPUTS; do
        echo "Verschiebe in $i nach $SINK"
        pactl move-sink-input $i $SINK
done

To return to alsa/pulseaudio sound I've got 'toAlsa.sh':

#!/bin/bash

SINK=`pactl list sinks short | grep alsa-card | cut -f 1`
INPUTS=`pactl list sink-inputs short | cut -f 1`
for i in $INPUTS; do
        echo "Verschiebe in $i nach $SINK"
        pactl move-sink-input $i $SINK
done

Sound Switcher Indicator

sudo add-apt-repository ppa:yktooo/ppa
sudo apt-get update
sudo apt-get install indicator-sound-switcher

While pavucontrol provides more differentiated options (default/fallback device versus per-application device), this tool simply changes all the above to one device, but provides easier access. Its unilateral setting can be refined in pavucontrol if necessary.