This is more geared towards youtubers who want to keep audio sources separate like for example not mixing in-game audio with the Tracker's Achievement sounds so things are easier to edit. For example an achievement sound plays just at the moment someone in teamspeak is speaking. Or so I can stream and record at the same time but remove the achievement sounds track in editing for specifically the youtube video.

There would need to be an option to Select the Audio Device. I don't know how difficult this is to implement, because not many applications allow it. PlanetSide 2 does it (and I only just discovered I could put in-game voice-comms on their own device too). And Ventrilo, TS3 and Skype have the option too (but that's kinda logical as they are voice comm software).

For example I use virtual VB audio cables to record from different sources, and each cable is in essence it's own audio device.

I record 5 Audio tracks currently

1: Loudspeaker (as a back up, but this has everything except microphone mixed into it)
2: Mic
3: Game Audio / Stereo Mix (=Anything not routed to a different Audio Device)
4: Teamspeak/Skype/Ventrilo
5: In-game Voice Comms

And hopefully my 6th track would be the achievement sounds from RTST.