It appears to be using an 1/4" patch cord, not an XLR cable! XLR is the cable (and connector) with 3 pins as is used with microphones and carries a balanced signal - 1 leg is ground, then the other two are inverted signals to minimize noise.
The way it works is so simple yet genius. Say the main signal is +x. Then one of the pins will carry -x. At the end, the receiving end will invert -x and add the two signals together. This gives x + -(-x) = 2x. So it gives twice the power. Great. So what?
Well, if you introduce noise into the chain, it gets canceled out! Pin 1: X + noise Pin 2: -X + noise
Final = pin1-pin2 = X+noise + X-noise = 2X
Brilliant.
https://en.wikipedia.org/wiki/Differential_signaling
I assume it's also the reason for 'bi-wire' speakers, while we're on audio gear.