Ok, I'm loving WMP, and all (or most) of its features, except one: Dolby digital support. It makes my music sound like volume goes up and down, its totally annoying. Maybe the problem is not Dolby, but, both winamp and songbird works perfect, so the problem is not my soundcard, or any other hardware/software component.
When in WMP, go to the 'now playing' view, and right click on album art, click enhancements, and dolby digital.
You can turn off any effects from that options menu.