Soo. First update goes:
k-ww tipped me off how to read the am27c256 EPROM chip on the controller and this post is about my try to this exact thing.
To read it i need a MCU with 15 adress lines and 8 data lines. For this i used a Atmel ATmega32 and my STK500 board.
Hooked-up it looks like this: