A tape monitor circuitry is quite retro. Who still owns a cassette recorder or a tape machine? Who still has an equalizer?
To put it another way: Who would like to do it and cannot do it because no manufacturer offers a tape monitor circuit anymore?
Well, those who want can again.
Today’s audio levels are much higher than in the past and many recorders will be overloaded by them.
In that case simply press the switch and the level to the recorder is lowered by 10 dB.
To compensate, the level from the recorder is increased by 10 dB. Et voilà.