A step up transformer for the preamp could be considered, because the pre is generally low on powerconsumption. The poweramp however is an entirely different story and you would probably need quite a hefty unit to do the job properly without serious losses in dynamics. I'd rather suggest, you contact your dealer or the manufacturer direcly on how to change the voltage for your units. More often than not that can be done quite easily by someone qualified to do the job. Hope this helps you on a bit.
Cheers,
Cheers,