What button directs the output of any fader to the DIR?

The DIR button is specifically designed to route the output of any fader directly to the Direct Out (DIR) stage. This function is crucial when you need to send a specific channel's audio signal to a different output for processing or recording, bypassing the main mixing path. By using the DIR button, you can ensure that the sound from the channel is directed to a dedicated output, making it useful for live sound reinforcement or studio recording scenarios.

The other options serve different purposes: the OUTPUT SELECTOR is generally involved in choosing what signal is sent to the output but doesn’t specifically route it to the DIR; A/B SELECT typically deals with selecting between two input sources rather than managing fader outputs; and MAIN MIX relates to the overall mix output, which doesn't directly affect the individual channel outputs routed through the DIR. Thus, the DIR button is the correct choice for directing the output of any fader to the DIR.