Ok, i will wait. In the meantime I found a dirty workaround: I monitor the plex process via [ps-watcher](http://ps-watcher.sourceforge.net/). If the plex process hit 50% CPU ps-watch will run a shell command. (and run enother if it goes back)
On my mac mini plex use 12% cpu while in menu or pause. while play 1080p it use ~70%.
For the light this could be enought, for my second [goal](http://forums.plexapp.com/index.php?showtopic=7264&hl=) (play 2 different sound track on 2 different audio interfaces) i guess it won't be very syncron.