Stepdown transformer 240v - 220v

Hi Guys
I have a integrated amplifier that is set for 220v European and i need to use it on a 240v outlet here in Australia , the amplfier transformer is rated at 500va and the amp is 100wpc into 8ohm
what size stepdown transformer would i need ?
i have seen a stepdown that is rated at 600w - 2.7 amps
and a 1000w - 4.5amps .
I wish to maintain the best sound from the amp and don't want to restrict its power supply .
sorry but i am a bit of a nuff with electronics.

Thanks for your help

Phil.

Regards
Phil