[asics10]

Im not a Touch Pro user (yet), but in WMP on my vogue you can designate a button that will shut the screen off without cutting out the music.

try this:
Open WMP
Menu
Options
Buttons
Toggle Screen - assign a button (camera button in my case)

When WMP is playing and on the screen, say with Sirius, I hit the camera button and the screen shuts off but the music still plays.

It may not be the same for the TP, but give it a try, I hope this helps.