Multi State Objects are always above other static graphics. You should put the 'static graphics' as 'overlay objects'. Group them, convert as a Multistate Object (two equal states, yes) and check Autoplay in Overlay Creator. Then, this group will show on the other (if them are in a superior layer).
okay but if the "static" thing is supposed to lead to the next step of the MSO, the button function seems to disappar once the layers are grouped as "overlay objects". ??
It's important that only interactive objects can appear above interactive objects.
Buttons are interactive objects you can put above a MSO (bring to front, or move to the top layer) without covert them in a MSO.
These articles may help you:
(sorry by my poor english)