Happy (not for you ...) that somebody else experiences the «sleep issue». After 2 years, I have found a way to manage this problem by playing around with AppleScript, Power Manager and Caffeine. I wrote a little idle handler that monitors the activity of some specified application. If those apps are using more than a predetermined level of CPU activity, Caffeine (that is scriptable) is activated and the sleep process is prevented because Caffeine resets the system's idle time.
While I thought that I had found a perfect work around, buying an Apple TV created a new problem. Streaming to the Apple TV from iTunes does not reset the system's idle time, so does not prevent the computer from falling asleep in the middle of a projection. Monitoring iTunes CPU usage does not work either ... the CPU usage is not amplified when iTunes is streaming to the Apple TV.
I created a not so perfect work around. I started monitoring the position of the mouse pointer to create a new condition activating Caffeine. Whenever the mouse is moved to the suspend screen saver hot corner, the handler activates Caffeine, thus reseting the system's idle time and also the sleeping process.
But I am still looking for a more complete solution, to prevent these 2 problems:
(1) I would like to find a way (shell script ???) to detect iTunes streaming activity automaticaly: not requiring the manual intervention of putting the mouse pointer in the hot corner is basic ... you realize the importance of this when the streaming stops in the middle of a projection and when you have to go in the den to awake your computer because you forgot to put the mouse pointer in the hot corner; it is more frustrating, if you forget that repeatedly;
(2) while streaming to the Apple TV, the screen saver should be activated without allowing the sleep process.
These 2 could easely be done by reseting the system's idle time when streaming. It should be a standard iTunes features, nor requiring any work around.
Well ... hoping this will help to bring a more perfect solution.