Without model numbers we can't give you an exact answer.
In general it sounds like you would need to connect the cable box and Sony HTS to the TV with HDMI.
Given that you have only 2 HDMI inputs on the TV I assume that it is old enough not to support ARC so you would also need to connect audio from either the TV or the cable box directly to the HTS to get sound from the cable box through the surround system.
The most common way to do that is to connect an toslink optical audio cable from the TV or cable box to the surround sound.