The Sony HTS has three inputs (HMDI-ARC, optical audio, and analog audio). I can't find any information about the TV that mentions if and what audio outputs it may have. Same is pretty true about the set top box.
So your options are
1. Connect the STB to the TV. Use HDMI if you can. Then connect the audio output of the TV to the HTS. If you don't have matching output and input you will need an active converter.
2. If the TV doesn't have any audio outputs then your only option would be to connect the HTS to the STB directly.