• There are too much volume controllers in a typical computer system
  • PCM volume
  • Mixer volume
  • EQ preamp (WinAMP, MJB)
  • Replaygain preamp
  
  
• No person is able to overlock this in a ways that
  • SNR is best possible
  • No distortions occure
  
  
• volume controls can have internal restrictions
  • granularity of settings (SB128: 2 dB steps)
  • Some distores below fullscale (SB Live!: -6 dB, lot of other -2 dB...0 dB)
  
  
• bass correction is needed for reduced volume settings due to Munson-Fletcher effect
  
  
• AC97 resamples to 48 kHz, this is often done in a poor way.
  
  
  
• There are a lot of other effect devices (Q-Sound, spatializer, EQs)
  
• There is too often quantized.
• High quality quantizing needs a lot of CPU power (1.5%).

There's only one volume control (instead of 2 . . . 4).

This is possible, the main problem is that you must change some things deep into the typical audio programs.