Comment by Trellmor

This is what I'm using, Shield => HDMI => TV => Optical => Soundbar. There are some settings on the TV to enable external speakers over optical, which format is sent (Dolby Digital, etc), and which format is accepted (bitstream) that you may need set. The Shield also has settings for which signal is sends. Works well for me after configuring it and I get Dolby Digital 5.1 (ac3 5.1) from my Shield to my LG C2 to my soundbar over optical.