I am currently using two computers on my desktop, one main computer and a laptop on the side working as a extra monitor, I control it via Mouse without Borders.
I am mostly using a headset when I am in front of the computer so to get the sounds of both computers in the headset I went looking for a solution. Initially I thought I would need some kind of virtual sound-card and then stream it to the other, it was much simpler than that.
I found SoundIt in the Chrome Web Store. It shares your audio via an easy to get to web site. After installing it I start it from the Apps in Chrome, setup to share my screen and open the URL I get on the other computers. That’s it! Sound it!