Samsung DLP set won't output sound to soundbar...

when using Chromecast. It's a HL-T6187S (this is NOT the same set I have mentioned in another thread, as I have 3 DLP's in the house, 2 of which are similar 61inchers, but not identical)

I have a Yamaha sound bar that has 2 optical cables installed: one for the TV and one for PS3. All of that works fine, but when I use Chromecast, there is no audio being sent from the TV to the soundbar. Do all TV's have this issue with passing thru the sound from Chromecast? I have tried the internal Mute either ON or OFF. Normally, since I got the soundbar, of course i have the Internal Mute set to ON.