Possible Solution
I too had this problem on my bootcamp MacBook Pro (with a RealTek audio device). I went to the "sounds and audio devices" control panel and turned the device volume down to "low" as well. Now the volume scales in a much more linear fashion. Previously, my last five or six notches of volume were at maximum.
Of course now I have the problem of readjusting my individual applications which I'd set up to compensate.
"Dear software developers, please make all volume settings universal. I shouldn't have to adjust the volume in eight different places to achieve a workable solution." Oh wait, that's just Windows!
Dear Microsoft, your market domination baffles me. How does a company which produces nothing but inferior unoriginal products dominate the market in such a way? Surely there must be some sort of criminal element, witchery, or other sort of dubiously ethical activity transpiring out there in dark, dark Washington. Boo to you
To the above poster, I am sorry I do not have a solution for you but the ear splitting volume of my Windows partition did set me wondering as well.