Unable to Overdub when Listening to First Recording

Windows 10
Audacity Version 2.4.1
Problem: I recorded a 5-minute track using my AudioTechnica condenser mike - sounds great (playing the piano for a song by Franz Schubert). The purpose of recording the piano part of the song is so that I can play it and OVERDUB myself playing the 'cello (the vocal line). However, I cannot get the overdub process to work.

I’ve tried to follow the OVERDUB instructions, but I just can’t seem to get it right. I must of COURSE be possible, but I’m too dumb to get it.

I think, I suspect, the issue is how I’ve got my microphones plugged into the computer.

a. The AudioTechnica mike is plugged in through a front USB port. I use this for making the first (piano) recording. Works perfectly.
b. THEN…in order to hear the recording I can do one of two things:

  1. LISTENING VIA HEADPHONES: I must (!) must unplug the mike in order to hear through the headphones. I plug the headphones into the 3.5mm audio jacks on the front panel of the computer, and I can replay and hear the recording of the piano part.
  2. BUT…if I plug in the MIKE then I CANNOT hear through the headphones.
    c. SIMILARLY: I really want to hear the piano recording through my independent speaker/amplifier. In order to do this, I UNPLUG the microphone jacks, and connect the speaker/amplifier through the same 3.5mm jack on the front of the computer with a male/male cable (3.5MM on each end).

THEN I can hear the same piano part recording on the speaker/amplifier.

BUT…I want to play the piano recording through the speaker/amplifier, so that I can easily HEAR IT and OVERDUB my 'cello playing with it. The moment I plug in the AudioTechnica microphone (via the USB port on the front of the computer), the sound disappears.

SO that’s the problem. I’m unable to overdub due to the microphone plub in disabling the playback.

Any ideas? I’m not very technically adept, so I suspect there’s a setting or a physical method that obviates this problem.

I would be grateful for anyone’s wise guidance. Thank you. AND…my appreciation for this forum and the developers who have done such a great thing with Audacity. Thanks indeed. And blessings of the Holiday Weekend. Best ever, Gene.

An USB-AUDIO-INTERFACE would solve all your problems.

It is connected to the PC via USB.

A good one offers:

Microphone Inputs (often 2)
Audio Input L+R for instruments
Speakers/Headphone OUTPUT for monitoring
Volume Level Knobs for each Input
Recording Level Sum Volume Knob
MIX Knob for mixing instruments together with computers Playback signal
Monitor Volume Knob for controlling the speakers/headphone volume.

price is from 30,oo EUR upto some thousands. My prefered is the PRESONUS AUDIOBOX (99,ooEUR).