The XP Volume Control (sndvol32.exe) has two bars that affect most of the sound that comes from my computer, the Main volume control and the Wave volume control.
With casual use I found that the highest distortion happened with Main low and Wave at max. And the least distortion when Main is at max regardless of where Wave stands. Unfortunately the main methods for accessing volume, buttons on laptops and convenient software controls, control Main.
There is a long term solution with:
Volume Tracker maps the Main setting to the Wave setting so they are always equal. (It can really be set to mirror any of the settings on your mixer if you wish.) This avoids the situation of having Wave very high, and Main very low, and limiting the amount of distortion you have to deal with.