But it is possible to use the top side fan or with that xigmatec it's impossible?
Well, i never used the stock panel with my xig, but looking at it through my windowed panel, the xig is probably only about 10 mm away. I wouldn't worry about it tho, i just put my to top fans as intakes, and the rear as an exhaust, and i'm getting 30 *C on my cpu and 45 *C on my gpu while running F@H GPU2.
Here's a shot with airflow arrows; my side panel fan is an intake too.
I like to have positive pressure because I have 2 dogs, so it helps to keep the dog fur out of the case