Just finished building the HTPC last night. All in all I am very happy with the choices I finally made, some of them thanks for this forum.
Before I will post pictures and details, I just wanted to say that the Slim X3 cooler worked like a charm. The brackets had to be installed on the cooler itself (not on the other side of the board). On the back side of the board I only had to add some rubber washers and screws.
The clearance is about 1-2 mm on one side, between the cooler and the capacitors. It was so close that I spent about 30 minutes with a powerful flashlight trying to see if the cooler touches the capacitors. I finally had to make a decision even though I was not 100% sure.
Pictures soon.