Unbalanced pre out to balanced amp in

I have a Modwright preamp with RCA outs and Channel Island amps with balanced inputs. I have always just made up cables with RCA outs and XLR connector inputs. But I have had to extend the distance between the amps and preamp and the new run has the cables going by a few power cords, a TV, an ethernet cable and other possible sources of noise. I would like to experiment with a transformer to convert the unbalanced output to balanced and then use 3 conductor cables for the run. Does anyone have any suggestions. And has anyone used a transformer they could recommend?

Thanks,
Mark.