What is the XLR pin out configuration?

The XLR portion is wired as L/R connections in accordance with the system originally introduced and promoted by Headroom USA for balanced connections.

Pin 1 – Ground
Pin 2 – respective channel Positive (+)
Pin 3 – respective channel Positive (-)

This is the standard XLR pinout.

This very different from the wiring of the 6.3mm jack portion, which uses one connector for stereo, the left one with the negative polarity output from the amplifier and right one with the positive polarity (normally that connector should be used for critical listening).

This 6.3mm connection allows standard headphones to be connected using a single 6.3mm jack connector (to either 6.3mm jack) while with the correct wiring two 6.3mm jack connections form a balanced connection.

Hence “Single Ended Compatible – Balanced”.