A cable is neither balanced or unbalanced in themselves, but how it interconnects what it is connecting. However, they are frequently referred to as balanced and unbalanced cables for the usage they are typically used for. The output of the Voicelive Play and a microphone with an XLR connection, such as an SM58 are 'balanced'. The 'MIC/LINE' input jack on the SX900 is 'unbalanced'. The cable I suggested is wired to provided a means to interconnect those two different types of outputs and inputs.
If connecting the SM58 to the input of the Voicelive Play, an XLR to XLR cable would be used and then an XLR to1/4"(6.3mm) from the Voicelive Play to the SX900. If connecting just the SM58 to the SX900, then the XLR to 1/4"(6.3mm) cable I suggested would be used
A balanced audio signal has two equal signal components that are 180 degrees out of phase and need two wires within a cable to make a connection. An unbalanced audio signal has only one component and uses only one wire within a cable to make a connection. The link below describes it pretty well.
https://www.aviom.com/blog/balanced-vs-unbalanced/Hope this helps.