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!
Please bear in mind that the Community is not an official Spotify support service. It's a place where we all help each other, whether we work for Spotify or not. So please use your discretion when using the forum.