You did confirm that you receive no keyboard error with the KE72T plugged in without the cables connected to breakout board, a keyboard connected through the pass thru port, and the keyboard works after you boot, correct?
When you connect the cables to either one or both the breakout boards to which your buttons are attached, you receive a keyboard error when you attempt to boot, yes?
You've confirmed you have Pin1 if each cable properly oriented?
And you have your panel propped right side up so multiple keys are not inadvertently pressed in closed position while booting, yes?
If yes to all the above, I would probably start with just one side connected to breakout board, unhook all the disconnects from the "hot" side of each button/joy, boot to ensure it works,then reconnect one at a time including testing the button press with notepad or some other keystroke test till you get an error.