The Onkyo can be used with speakers that are 4 ohms or higher. The speakers from the Sony GN1200d are 6 ohms so are safe for the Onkyo. However the power rating of HTS systems is basically a lie so you will have enough power in the Onkyo to damage the speakers. Be careful not to blow them.
You will also have a problem because HTS systems have an amp built into the main unit for the subwoofer and AVRs don't. So you will either need to get an external amp or a self powered subwoofer (the better option).
Plan on replacing the front L-C-R speakers as your next upgrade.