if thinking of getting a system 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 and i want to use a 7.1 channel headset. Does that mean that i would feel no difference in terms of sound if i used a 5.1 channel headset?
More than likely, it's either a USB headset, in which case you're screwed since it wouldn't use the sound card anyways, or it uses VIRTUAL 7.1 surround, which means that paying for a sound card is an absolute waste. *(Which it might be anyways - nicer motherboards with the realtek 898 audio codec are 7.1 surround with optical out anyways.)
USB plug, 7.1 digital: http://www.engadget.com/2012/01/05/plantronics-gamecom-780-7-1-surround-sound-gaming-headset-han/
Two questions:
1) Do you already own the sound card?
2) What motherboard do you have?
Like as not, that sound card is pointless - it's so cheap that the integrated sound card on your motherboard might even be better. Generally there's not much point to sound cards until you start hitting $100+ because there's little difference between onboard sound and low-end sound cards nowadays.
so i shouldnt get a sound card. What if i am not using the headset will i still hear sound?
Well... If you have speakers, you'll be able to use those. I mean, the motherboard already has a sound-card built in - you can plug speakers, ect into there.