Toslink is only going to be worth it for any source that is not already HDMI, such as cableTV or OTA antenna, or legacy video games capable of discrete surrounds with optical out onboard (Wii, gamecube) .
I use toslink on my TV with my antenna, gets me 5.1 audio for free!
Right... Like i said.. Straight cable..
Or antenna of course. However, sadly cheaper HDTV's won't always push 5.1 from port.