How to assign applications to different sound outputs

Hello,
I use my pc to watch movies. It is connected to my tv via hdmi and sound system via SPDIF optical cable. Everything works fine, but sometimes I want listen to music or other apps through my headphones, while someone else listens through sound system.
How can I do that?

Windows 7 volume mixer shows both outputs and I can control the sound of different apps and mute them, but I can't assign specific applications (music player, browser) to other sound outputs.
One time the browser was assigned to speakers (headphones) rather than SPDIF, but I couldn't assign apps myself.
Thanks in advance.

I have only onboard sound and strangely I could hear two different streams at the same time. My brother was watching a movie via home theater and I was watching youtube videos, hearing them through headphones. So I know it's possible, don't know how though . Maybe because the pc doesn't actually encode the movie audio, it only streams via spdif cable and the home theater does the rest.
I'm just trying to find a way to assign a browser to simple speakers rather than spdif and not disturb people watching a movie.

Hello, I have USB speakers and onboard, I like to play spotify in the USB speakers and other stuff on the onboard SC.
but all applications just follows the default setting