[dOm1naTOr]

@king rrr
yaarrr, me too have the same mobo. The obboard sound of it [Realtek 850 HD 7.1] is gr8. Its HD audio ready and have good features like Jack Sensing, Universal Audio Jack etc and its also EAX 2.0 ready. I think its some what close to Creative sound blaster [which is at 1.3k] in terms of perfomance.
Also ur onboard has much more features than the creative blaster, like optical, co-axial, SPDIF outputs.
Consider buying a sound card only if u have a top notch speaker[whether a 2.1 or 5.1 or 7.1] which can reproduce all sounds as its meant to be heard[probably a THX one]. Else u won't notice any difference.

Its not with no. of channels [2.1, 5.1, 7.1 etc] that the perfomance of a good sound card lies. Its perfomance is for its decoding of sound and produce uniform amplification at all levels of sound without distorsion. Also it has major role in frequency range. A good sound card has the widest frequency range. But u shud need a speaker that cud produce all that frequencies[Like the Logitech Z5500 THX].
Its gr8 if u have a high end 2.1 [from Bose, or Clipsch] and to get full perfomance from it, u will need a high end cound card like Creative XFi- Xtreme music, or Elite Pro.

Hope this helps buddy