[songpony]

You would have to buy an external device for this. I got a unit for about $80 - it's really lightweight, and has multiplex capabilities as well as key control. I just run the audio of my PC through it - you could even use it to key-change Hoster songs if you wanted to. For the most part, I don't even power it on until I need it for a WMP song - turning it on and off has no impact on the audio of a playing song, and it's super easy to use. Let me know if you want any further details.