Sound from xbox to computer

I am currently using my xbox 360 sound through the computer to work with the
headphones that I have plugged into the computer. I just got a new desktop
and when I use the headphones, the volume is too high and when I try to
adjust it using the sound on the computer it does not affect anything exept
when I hit mute, then it will mute the headphones which are playing what is
on the Xbox 360.