Not sure if I have seen instructions for the MDD anywhere. I have only seen info for the
Sawtooth and the
Quicksilver. Reason probably being that the MDD are not popular among modders. Personally I have done a G5, a Q4 QS (info thread soon) and I am in the process of doing a G3 b&w. When I ordered a G4 MDD on EBay however I quickly realized what people mean when they say a MDD is basically impossible to mod.
Even without knowing your specific situation with the MDD my recommendation would be to ditch Apple's original front board and create your own with standard PC parts, which is what I did with the G4 QS. You basically re-create the front panel board holding the switches from wood or plastic. In my case I did a 3D print. You then use kits like
this or
this, if the front panel switches of the MDD have enough travel. The switches in the G4 QS did. The switches in the G3 b&w not so much though. There I created the front panel board with a 3D print and then soldered contact switches like
this to an existing cable kit like the ones above.
Pictures of the 3D printed parts attached to this post. What you see there from top left to bottom left: 1) USB/audio front panel for the G4 Quicksilver, 2) holder for the flat contact switches + LED for a G4 QS, 3) holder for physical Lian Li switches for a G4 QS, 4) holder for flat contact switches + LED for a G3 b&w and G4 Sawtooth.