Hi,
I'm Rodrigo and I'll help you.
There are many options for this task, one of them is connecting a 3,5mm cable to the audio output connector, and the the other side to the audio input on the other computer. On the receiver computer, go to Settings > System > Sound > More sound settings > Recording tab > Double click the audio input device > Listen tab > check the "Listen to this device" box > Select the output device > OK.
As I said above, there are many possibilities to achieve this task. Please let me know if this one is good enough for you or tell me your current setup so we can improve it.