multiple data into single DAC converter

[pkd0057]

Dear All
i Hve a quarry ,
When we are playing  two song from two player in a PC then how dac of the sound card acts , that mean how datas are send to a single DAC so that we can hear both the song at a time.

I am trying to generate two sine wave from a single 8 bit dac , i am not getting the way pls suggest me.