I am going to assume that you want to use the speakers from the Sony HTS.
The Sony 3 front and 2 rear speakers can connect to the speaker terminals of the Onkyo if you remove the Sony connectors from the speaker wire. Make sure that you keep the plus and minus wires connected the same way for all of the speakers.
The Sony subwoofer however is not self amplified so leave it connected to the Sony.
Connect the subwoofer out of the Onkyo to the Sony main unit analog input and that should drive the sub for you.
All your sources go to the Onkyo receiver.