How to connect my pc audio out and set top box audio out to same speaker

[raruntvm]

Hello All
My name is Arun. Iam planning to set up a pc system and this is the way it should work.
I have a sony EX 330 monitor. am connecting my setop box video out as well as pc video. Now i want to connect the set top box audio to creative 5.1 and pc audio to the same speakers. How it should be connected. if you have a solution please explain it. thanks in advance

 

[ssddx]

depends on what outputs the set top box has....

provide some details.