@dawid This just means that they don't sell a balanced cable. Or they may be saying you can't adapt the stock cable, which is also true, you can't adapt a single ended cable to balanced.
Any headphone that takes two separate wires to each cup by definition, you can make balanced, balanced is just two distinct wires to each transducer and how can you not have that if the two cups aren't connected to each other across the headphone? The only headphones you have issues wiring balanced are single sided entry headphones, where there are only three wires going in. If the two cups are independently wired, you must have an independent + and - and so you can make them balanced.
The distinct thing that the R70X does, with the stock cable, is it wires the stereo signal through to both sides, all three pins on the TRS are connected both sides, so you can connect the R and L either way around. It's a 6-wire cable rather than the usual 4 with just the grounds joined in the jack, this one, the left and right also go to both sides cups and are joined in the jack (or the Y split, but I suspect, the jack).
You CAN replace with a balanced cable, but you lose this function, as with the balanced cable the grounds are now distinct, you have a L- and R- going to different places. So the balanced cable has an actual left and right side, make sure to mark this, and you need to connect it correctly to the correct side (you'll actually get no sound if you put them the wrong way around, rather than it inverting, due to the TRS pin configuration).
The wiring of the 2.5mm TRS on the headphone side, the ground/negative for both L/R is the (S)leeve. Right+ = (R)ing. Left+ = (T)ip. I.e. it's standard stereo wiring. I have these here, with a 2.5mm balanced cable, I checked this.
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