This is Sparta! (umm, Windows.)
https://discussions.apple.com/thread/4271460 kicks around how iTunes may be able to add this feature. Windows has been hit or miss in this area.
Can I play music on my PC, at the same time as I'm playing a movie, and only have the music heard on my Bluetooth speakers?
I would like to play music on my PC to be heard in another room over Bluetooth speakers, and not have the sounds from my PC heard too. Is this doable?