I would suggest you buy step-down transf. 240/120V. Sized the capacity with NLT 25% to allow in-rush. I think your Onkyo has HCPS. 1000VA 240/120V transf. will be appropriate unless you connect more loads. Put surge protector as well for power surges NLT 360joules. If your area has frequent power noises, then better provide a 1500VA UPS autovolt 120/120V or 240/240V in & out and plug this to the output of the Transf.
In this case, your transf. will not only act as the step-down, it will become as isolation transf. to isolate any disturbance. There you can attain high power reliability and PQ. Better plug your HDTV & bluray player there as well.