NAC 202 MUTING RECORD OUT TO IMPROVE SOUND QUALITY

Just got a second hand nac202, tried to mute record out but not sure if I'm doing it right. Press "Mon" followed by press the "Mute" button doesn't seem to work. I then went into "program" mode, doing the same 2 button press lit up the "Mute" button for about 3 seconds and then it went out. This is not quite what the manual said:  "To engage or disengage record mute press the front panel mon button followed by the front panel mute button. The mute button indicator will illuminate when record mute is engaged and extinguish when it is disengaged."

There is an old thread about this topic, which is close right now: https://forums.naimaudio.com/to...sound-quality---help

Any help is appreciated.