I decided to shape up the digital dashboard a little bit. I made a base board for the Arduino Nano with socket header same as the TM1638 displays use. Added external power supply jack with 5v regulator, in case the arduino is connected to a USB hub and can't draw lots of current from the USB.
Changed the code to improve the serial communications. Custom baud serial speed of 125kbps. Now its stable enough to run with delays of 1ms along AMC644USB without running out of buffer space or freezing because of the high speed 16-bit data transfers. This change was mandatory to be able to have the x-sim USO running all devices (AMC644USB + Dashboard) with delay of 1ms. Among others added some extra code for flashing the shift indicator lights without delay, just by using a custom timer.