A simple matter. Look for the amplifier cube on the board. Check the model and find its technical data, in them the output diagram and enter the pin numbers. Refer to the specifications for the speaker output impedance range. Knowing the cube outputs, find on which pins of the d-sub socket they end and solder the satellites with the appropriate impedance there. Based on the photo of the MESS7 user plug, make a mirror image and knowing the position of the amplifier outputs [OUT P, OUT L, GND (amp)] determine where to solder the power switch (pins + 5V and ON).
