With the low end Sony's, like the one I have, the HDMI is not decoded by the receiver at all. The HDMI is only a straight through switcher, sending the selected HDMI to the screen. To get the sound from the source playing on your receiver speakers, you would have to connect the sound from the source via optical or digital co-ax too.
So marco79, the only way that you could have only one HDMI cable between receiver and screen, is if all your sources were connected to the receiver via HDMI. To get the surround playing on the speakers, you would need a optical or digital co-ax between each source and the receiver too.
That is why I am upgrading our crappy Sony receiver as soon as I can.