Slider displaying over the main menu in Enfold site

On the site I’m creating, I’m unsing 2 sliders one above the over on the homepage:
– the first one contains animated pictures and texts
– the second one is just a grey headband with text for an announcement.
(see there: http://www.homelink.fr/wp/)
I’m using this second slider because it is the only way I found to spread this info on the whole width of the page over the left widget and the main content.

The problem (only on pc Windows, not on Mac) when you scroll down the page, is that contents of the page go over the menu ( I setup a fixed header on the theme options).
At the beginning (on Mac), I only notice the problem with the second slider (the grey one) coming over the menu and I solved it with a custom css (z-index: 1) in the LayerSlider general settings. It works but only the slider.

Any idea to explain and solve this problem of display?
Thanks for help.