Handling your audio volumes while doing a live stream using software, not hardware. Is this possible

Basically I stream my community tournaments and I don't have a physical mixer. I would like to control the volume of my game audio, headphone audio, and mic audio all separately using some sort of software that will do it WHILE I am streaming.

What options do I have?

Edit- Running Windows 8 and would like to have total control my audio volumes. I am also using a laptop to stream but it doesn't have a fancy sound card.

Edit 2- Realtek HD is installed and I use xsplit