I use a stereo mini plug into the headphone jack of the computer using both red and white (Stereo) and connect to a line-in channel on my mixer, again using a stereo adapter, that has individual channel EQ, Reverb, Etc. just as my mike channels. If you only use the left side of your mixer, you can't get stereo sound. I never use the tape/CD in/out connections. Using a mike/line in connection gives you the same EQ, reverb, etc. control as using the left only, except you still have stereo.
muzicman