Hey with this sound card - Asus Xonar DG PCI Gaming soundcard, 5.1 Channel, Dolby, Up to 105dB, Built-in Headphone AMP,GX2.5 for realistic 3D audio, Low-profile bracket included. What does 5.1 channel mean? Does it mean i can only use 5.1 channel headsets and not 7.1?