Outstanding Audio/Video Quality without updates and muffled/"sandy" audio with the most of post 2009 updates

[Dixel]

Short story : just like the topic says . 

Longer story : I'm a sucker for great audio and video ! No wonder it was my job since the early 1990s. I have an audiophile sound card (several , actually) .

 On a clean Vista (with any official SP) the sound quality is fantastic ! Also, the video quality is full RGB and with rich and vibrant colours , but as soon as I install

almost any update after the platform update , it becomes terrible , muddy , muffled , sandy sounding . Like it's having an obstacle (a pillow) , for example.

Have you ever encountered something similar ?