In Windows XP I could, for instance, play music on my speakers then have a game play on my headset via this clunky method:
- Set default sound output to speakers
- Run music player
- Set default sound output to headset
- Run game
A 'feature' of XP's audio workings was that once a program launched and grabbed some audio output, it would always use that if it was multi-output naive (most programs), while some others (e.g. Skype) could list and pick particular devices. However, in Windows 7, whenever the default output changes, every program using 'default device' dynamically changes via stream switching.
My rationale for this is that it allows me to easily change the volume of my music with the speaker knob on my desk while playing a full-screen game. If iTunes or Zune Media Player can capture keys or whatever to control volume (I don't care if ABC Media Player can), that would be helpful to know as well.