I would say yes as the Sony speakers are 8 ohm nominal, they do have a proprietary connection that would need to be cut off. The subwoofer from the Sony is not powered, do not think it would work with the Onkyo.
ANy particular reason you want to hook up the Sony speakers rather than using the Onkyo speakers? I really don't think you would see any improvement in sound quality. It may well be worth trying though cutting off the Sony speaker connections may cause issues if you ever want to use or sell the unit.
Regarding the connections, if a sub from a HTIB was separated from the system and the connection that the speaker wire had from the sub had a termination connection only unique to the HTIB's input were to be cut, could that termination be converted to something compatible with the Onkyo receiver, assuming the sub was powered?