Single conductor with shield cables are unbalanced and work only up to about 20 feet. There are actually two conductors, but one of the conductors also acts as the shield meaning that noise is being shielded by the same material that acts as one of the conductors. The longer the cable run, the more noise appears in the signal.
Balanced cables have two conductors plus a shield.
This allows the signal to travel along the two isolated conductors and the noise along the shield resulting in a much cleaner signal over a much longer cable run. The processing units in a system use the same types of cables that are used in the input section. Microphones use XLR 3 pin balanced cables and connectors. These are low impedance and can be used with much longer cables, up to 200 feet. This will match the output of the keyboard to the input of the mixer.