Ok… Since you ask 
the idea of electric circuits like audio is about electrons moving out from one source and coming back on another. It’s a flow of electrons and the number of electrons that flow is decided by what ever is driving the process in our case two little amplifiers on the audio card…
Because most of this stuff came out of microphones and such like way back when the earth cooled it tends to be quite low voltages and so a full range audio signal probably gets to about a couple of volts at most, which isn;t really very much.
This voltage pushes electrons down the wire throu a resistor at the receiving device, and the current that flows in the wire and back to the source down the other wire obeys ohms law V=IR so the current in the wire turns into a voltage at the receiver which can be amplified or if it’s Britney spears rejected . . .
So all well and good but what about that smallness? IF you place the cable next to a spark generator or such like the laws of electrostatic induction come in to play … ( Guy called Gauss, lousy first lp ) and you will here clicks on your audio as the sparks induce extra currents in the cables you are using … Not good especially in the noisy environment of a stage or such like . So a solution was found. Part of Gauss’s discovery was that an electric field cant affect anything inside a conducting surface. OR to put it another way the effects of the spark don’t produce any effect inside a fully closed metal box ( Faraday Cage). So since one of the wires in our audio circuit ( the return wire) is actually connected to the o volts terminal of the Power supply in our device then we can wrap this conductor all the way around the precious signal wire and hey presto sparks rejected ( or at least heavily reduced )
This is shielded cable and you will see it all over the domestic audio workd with connects like the RCA phono type or common jack plugs which make a lot of effort to ‘shield’ the inner connector.
Look at a jack plug and you will see it’s actually constructed to protect the signal connector right to the tip…
So all well and good but shielded cable is expensive and also has other electrical characteristics that make it difficult to run very long lengths and it has one other problem
Magnetic fields
Magnetic fields don’t give a stuff about the inside of conducting boxes and flow throu’ then regardless, and worse on most stage there is a lot of electrical mains hum from lights especially at 50 Hertz or 60 if you live in the uncivilized bit of the planet.
So how to deal with this…
well the solution is quite clever.
If we send two signals wires to the far end and come back on the same conductor we have threee wires and mains hum will affect both the signal wires similarly and produce hum but if we invert one of the signals and then reverse the other one at the receiving end THEN add these two signals together then we have + plus signal that will be interfered with and a - minus signal that will be interfered with but when we invert one of them and add them together we get twice the signal ( 6dB (dont ask…) is actually a doubling of signal , which is why your original problem looked like a wiring issue ) and also the induced mains hum will cancel out !!
and that in a nutshell is how balancing works …
There are two basic ways of doing it electrically
One uses electronic amplifiers to do the inversions and additions and these are obviously pretty good but require power.
The other way is using audio transformers which do the same thing as all this but don’t need power. They also have a ‘nice’ response to being overdriven that audiophiles can get quite excited by. . .
Obviously this is more expensive than simple pair of wires and also tend to be delivered on Proper connectors so it tends to proliferate on Professional kit where signals can go great distances with in a company and are almost gaurenteed to be in hummy environments.
The Humbucker guitar pickup uses a similar technique to reduce the hum on electric guitar pickups … Hence the name
Hope this helps .