There's a Tutorial in your start menu, and various threads on this forums relating to how to set Ableton Live up for multiple outs.
Search is your friend.
http://www.infekted.org/virus/showthread.php?t=30368
For the Sidechain input refer to Vocoder or FX input in the manual on how to set up the inputs on the Virus.
It has nothing to do with your preferences/soundcard inputs, remember this is a hardware synthesizer.