I2S Bluetooth Transmitter
Such boards can be connected directly to the I2S output:
But to do this, #define SR_48K must be activated in Audio.h so that the I2S frequency is always 48KHz.
If you still have an old ESP32 in your box, you can use it to simulate this board. PSRAM is not required.
The BT transmitter is the slave and is connected in this way, the DAC serves as an analogue output, but is not necessary.
The ESP32-A2DP library is used by P. Schatzmann, https://github.com/pschatzmann/ESP32-A2DP.git
As the I2S output of the audioI2S library not always outputs 44.1KHz, it is scaled internally to 44.1KHz for compatibility. 8000Hz, 22050Hz, 44100Hz and 48000Hz are possible. This is necessary because the ESP32 BT library expects this sample rate. This means that old BT devices can also be used. It doesn't matter what sample rate the audio source has.
Test circuit: the audioI2S library is running on the left, the BT transmitter on the right