Yip...it won't work that way! From your DSTV you go (audio rca cables) to the Sound bar and leave the hdmi to your tv. when you want sound bar sound, your tv sound must then be on "0"...
You can either connect the soundbar via the audio out on your decoder using the red and white rca cables , but your tv probably has an audio out either a auxiliary out or rca , make sure you use the correct ports ( your tv manual should tell you)
Oh and don't forget to check the setting on your tv
Pros: SB plays audio for all TV sources whether external HDMI (e.g. DSTV Explora, Chromecast, PS3) or internal (e.g. TV DLNA media player, Smart streaming apps).
Cons: All audio is only stereo (PCM), no 5.1 surround (i.e. no 5.1 HDMI in->optical out, I believe a limitation of my TV). Not a major issue as SB is only 2.1.
BTW: Samsung PS51E550 TV -> Samsung HW-F455 SoundBar. So no surround from this set-up, but rather a decent increase in audio volume and quality (specifically bass) over the internal TV speakers.