They are the same exact card, except the zs has 7.1 chanels and a higher signal to noise ratio. Audigy2 has 6.1( i believe) channels and a differant DAC. Go with the cheaper of the two since you only need 5 channels plus subwoofer.
I got my Audigy zs at my Local "Worst Buy" for $59 after rebate. But since they made a mistake on the sign they gave me $40 cash back on site.
