Surf Cable's make a balanced cable for the R70X here
https://www.surfcables.com/collections/cables/products/audio-technica-compatible-cables . I been using there cable for a year and five months give or take.
it does alright when you don't have issues with the braided sleeve, I do wish those cables on eBay existed back when I bought my R70X, so I could have saved 90ish dollars. Just so you know surf cable's are not cheap, they charge $120 dollars for 4 Feet, $140 for 5 Feet standard cables and then offer $200-$240 for OCC.
My experience is only with the standard cable since at the time of buying one that was the only choice they had back then, but be warn the braided Sleeve material that they use on the cable is cheap. It has a habit of coming undone from each other, or breaking exposing the wires. I had it happen to me twice both with the original cable and the replacement they sent. Also it's very easy for the cable to lose it shape. Beside that I did had to get the cable replaced due to it causing issues with the sound, so far the replacement doesn't have the sound issue but it does have the same braided sleeve issue. The braided sleeve is used on the whole cable including the R70's 3.5 cable Y split.
I don't know if they still use the same material, as I haven't bought another cable from them since then. They also so far seem's to be the only usa company that make's a balanced cable for the R70X that I know of.
Edit: I don't recall what the R70 sound like in Single end since I been using it strictly balanced for a very long time.