Please explain balanced outputs

XLR=Balanced
RCA= Single ended
Except that some amps and/or pre-amps have XLR connectors and do not have balanced circuit design. Basically its just an inboard adapter. Balanced cables have better noise rejection on long runs. Truly balanced circuitry in an amp or pre-amp will have a lower noise floor. Some companies (BAT for example, use all balanced circuitry) Others just accept both types of connectors.

When both sides are balanced this is the better route. Swampwalker is correct that many amps might have XLR inputs but they are still unbalanced and a special circuit will compensate. When this is the case, use unbalanced.