I know that this is technically possible and probably is just an unpublished registry setting so here goes:
Windows Media Player
in Windows 7 has a remarkable little feature few probably know or care about
This little gem allows me to specify which of my sound output devices Windows Media Player uses. When I plant my ample ass in my supple leather desk chair I desire output to my desktop stalwart Altec-Lansing ACS90's by way of my mainboard's inbuilt Realtek audio. When my wife in the next room wishes to explore the bounty of internet programming that I've convinced her exists cost and problem free through the glory of Windows Media Center, she hears nothing and I get her audio track played to me in my isolated fortress of DOOM (the next room). Let it be said that audio track programming of "Say Yes to the Dress" over the death squeals of my vanquished must be stopped primarily because it throws me off-game and secondarily because the wife must learn to lip read.
The solution is, knowing the common lineage of WMP and WMC, find where I can set WMC to select it's audio output device as WMP does. Simple enough right? I mean somebody made a Kinect connect to a PC recently. This shouldn't be rocket science for you smart folks, right? A bounty will be considered providing nobody writes any code. Let's call it a finders fee. I already wrote the background app that switches the default audio device based on usage. That approach won't work. Find me the grail.