No surround sound output for some HD channels

Hi All,

I have samsung 43K5570 TV. Using Sony HT IV300 speakers. TV input sound is fed into Home theater using Optical cable only. This is my first home theater and dont have much idea about the functions and everything.

Recently discovered that when selecting "CLEARAUDIO+" mode, SD channel's 2.1 sound is converted to 5.1 and we get the surround sound in all 5 speakers. But when selecting HD channel lets say "Star sports 1 HD", the output comes only in 2 speakers and no surround sound. Observed this when watching cricket.

But strange thing is, the surround sound is observed as soon as the Ad starts and that too for only 1 second. Again it falls back to only 2 speakers. So it means the channel does support 5.1 output but still no surround sound is observed for HD channels especially. Observed with Zee Studio HD too.

Ideally HD channels should seamlessly output 5.1 surround sound. But SD channel's 2.1 is easily converted to 5.1.

Not sure how to set this up. My understanding is, all HD channels will output audio in surround sound(5.1).

Should I use HDMI cable only to get good surround sound for all channels ?? Please help on this.

Thanks in advance,
Vinay