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As a side note, basic entry level audio interface do allow this :
They do have an analog mixer knob on the front panel effectively mixing the analog input signal with the playback signal. So you get full time input monitoring without complication and you can set the amount of direct signal you want in the headphones.
Some other basic interfaces do have a Direct Monitor switch that does the same thing, but with a fixed mix ratio of 50/50.
So it seems to me abnormal that high end DAW software used with high end audio interfaces of the same brand (MR816CSX, UR824, Yamaha Nuage I/O interfaces…) cannot replicate this without complication (without creating another audio track dedicated to input monitoring).
So basically we need the capability to mix input monitor with track playback, and get independent level control for both signals. This should be managed on a single audio track slot.