When I say bitstream I mean this:
If you connect your computer to a receiver via HDMI, the receivers DAC would decode the audio. The volume slider wouldn't work (if the volume slider worked, it wouldn't be bitstreaming). This is because then the audio feed wouldn't be touched before it came into the receivers DAC.
Of course your audio card needs to support this (and newer graphics cards supports this).
Spotify isn't really a audiophile player. 320 kbps is not "high end", but at least bitstreaming support would make Spotify 10 times more attractive to audiophiles!
Changed back to "new idea" status - once this idea reaches 40+ kudos the Spotify staff will review it again and decide on a new status. ;)