I have a Senneheiser dongle that came with my headset. It's basically a soundcard in a small package.
the 5.1 on the dongle you posted is simulated using stereo.
you would normally use something like that if you have a headset with 3.5mm jacks and don't have ports on the front of your PC or on your speakers.
Keeps you from having to go behind the PC and unplug your speakers and plug in the headset.
Or if the onboard sound or soundcard failed, you'd use this as your soundcard.