I managed to get the PS3 working now without having to use the splitter.

The receiver mode for the PS3 was set to "Through", which sounds logical to me, that it lets the signal pass through. But in that mode, the receiver makes a conversion of the resolution, meaning that he signal is not passed straight away to the beamer. So I set it now to "Direct", which lets the signal through without doing anything, thus passing the video signal directly to the beamer, and playing the audio signal just fine. No need for a splitter and toslink cable anymore.