Hey All

I dunno if this has already been posted but this works 100% for me.

I have the RME fireface 400 connected to my 12 core 2010 Mac Pro and my mac was refusing to go to sleep automatically, it would sleep if i hit the powerbutton or selected sleep from the apple menu.
If i let the screensaver kick it wouldnt go to sleep.

I found this program called 'Please Sleep' http://www.macupdate.com/app/mac/29778/pleasesleep

Install it and it works with the energy saver prefs and now both my 27" imac and my Mac Pro go to sleep properly

I know its not a solution but its a viable workaround.