I've just downloaded MB yesterday as i was looking for a an alturnative to wmp.
I have a small audio & video studio and recently changed my audio monitors for a pair of Adams A7x's only to discover that the sound quality from wmp was poor compared to my audio mixing software (Nuendo). This difference I didn't hear so much with the old monitors.
I ran the first cople of songs using the windows audio, i think direct x or with a Windows MME dirver or something and it sounded only slightly better than WMP, i then changed the driver settings in MB to ASIO as I have an ASIO sound card (RME Fireface 800) and the sound was astonishing. I had never heard a consumer software sound as good as MB.
It is importanat to note that music software such as MB is set to the ASIO driver of the ASIO sound card for it to bypass the windows audio completeley. So, in essence, MB comunicates directly to the sound card without going through windows sound to deteriorate the quality.
The only issue i have with MB is my media controles on my logitech keyboard don't work when MB is not in focus, but Im sure it will be sorted in time.