A good soundcard needs two things: Good Digital to Analog Converters, and good drivers. As for specific specs, you want a high Signal to Noise Ratio [SnR], a large dynamic range, and low harmonic distortion.
You got a price range to work with?
Thanks for the explanation and as per what you explained i found a sound card. CREATIVE SoundBlaster AUDIGY Value 7.1 Sound Card.
is this any good? there are other cheaper options but this one has better specs..