How can I use 5.1ch?

I'm using Windows 10 and Unity 5.4, and would like to use 5.1ch sound. I set audio manager --> default speaker mode at Mode5point1, but no sound comes out of some of the speakers. I already tested the speakers using an different desktop application and they worked properly, so I do not think the speakers are causing the problem. Do you have any ideas what I should do?