Line-out analog signal converter?

Question

Do it yourself

You need a converter of the analog audio signal coming to the headphone line output (without preamplification) into a signal that can be fed directly to the microphone input.
Purpose: to ensure a minimum of distortion of the original signal.
Task: to feed a pre-prepared (mixed) audio stream to the physical microphone input.
How it is being solved now: a stupid “electro-acoustic decoupling” - the speaker and microphone were placed in one soundproof box.
This, of course, is too “lamer” (and rather cumbersome) solution.
I would like to have something more compact (and technologically advanced) like a simple resistor or (or some simple transistor amplifier / attenuator) that would not require the generation of sound vibrations.

Answer 1

Make a voltage divider across two resistors.
The following conditions must be met:
The voltage at the output of the divider (U2) corresponds to the input voltages of the microphone input
The resistances R1 and R2 are much less than the input impedance of the sound card
The sum of the resistances R1 + R2 is not less than the recommended load resistance of the sound card.
Something like that.
PS:
And the speaker into the microphone ... yes ... You know a lot about perversions :-)!