frederf is correct that you need to find out how to play Media Centre from the command line to use the custom playback. To save time (and more messages) here is what works for me:
MC18.exe /PLAY "%1"
Type this EXACTLY. Add nothing. Type this in the box under Custom playback.
For queing type exactly this in the box under Custom enqueue:
MC18.exe /APPEND "%1"
Then ask yourself why you aren't using Media Monkey, which does everything Media Centre does AND syncs iPhones, iPod touches AND has a version just for Android devices. (I have no connection to Media Monkey other than being a satisfied customer.)