Tried this last night. Was hoping to hook up my PS3 and Satellite receiver to my stereo system. I hooked up the TV first on its own without the toslink splitter and it works just fine. Attached the splitter (again only the satellite hooked up) and the sound would cut in an out. Tried the same test with my PS3 and no signal is received by the receiver at all.
I think in theory this can work. I do believe it is just mirrors that redirect the light from the cable. That said, when I looked at the amount of light which comes out of my cables, going through this splitter, it gets very dim. This is probably the reason why the receiver has issues. Too much of the signal is lost. I suspect, which very high quality optical cables, this may work.
One other thing to test before you try, is to ensure that turning off your equipment also terminates the optical signal. PS3, no issues but my satellite receiver, even when turned off, still sends a signal through the optical cable. It does not emit sound, but it does send light which would interfere with the PS3 signal is I was trying to use my PS3.
In the end, I will just plug and unplug the satellite optical from the receiver when I wish to have the surround sound and just keep the PS3 hooked up most of the time.