I found this very good tutorial about case & buttons reusing...

Then I decided to try by myself.

Then I connected all buttons to a Sparkfun SX1509 I2C I/O expander.

Hi, today I mounted the 2MCUs together...

It now looks like this :

From bottom to top : we have the 2x ESP32, the GPIO expander at center, then the 320x240px TFT w/ legacy GameGear controls PCB on sides.

a small overview :

buttons are responding & bridged screen works !

Hi, last week : I added the MP3 Module (DFPlayer MINI) & wired 2x MCUs USBs + added a LED @ same place than original one.

So we have the MP3Module on left side (linked to #2 MCU), BUZZER (linked to MCU#1) on right side & 2 USBs to control BOTH MCUs (via ArduinoIDE) + a micro female USB to power the whole system (@top)

So it can now play BEEPs & MP3 Tracks !

Today : started PWR managment board :