XLR to RCA to XLR

I decided to try the KUBE (KEF's equalizer) with KEF R104.2s in a balanced system. By careful routing of cables my system is silent to an ear at the speaker. But the KUBE has only RCA connectors, and adding it to my system introduced a sizzle, a kind of HF hum. I removed the KUBE, and silence returned. Is there any way of going from XLR to RCA that might avoid the noise?

Balanced lines (about 15') run from a Cary 11a processor to a Proceed Amp 3 that sits near the R104.2s. The third line to the center speaker did not run through the KUBE and thus remained balanced.

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