The way I'm seeing it, you just need to make the hole through the 40mm deep mdf, and the remaining 36mm of the tweeter is protruding from the hole. So the 40mm depth shouldn't be a problem.
I've attached a reworked version of your image.
I would use a normal circle jig and rout 3-4 concentric circles at varying depths. It looks like you already have the ability to work out what depth to rout at particular diameters.
Start with the shallowest cut on the largest diameter, and work your way in to the deepest cut at the smallest diameter.
In the pic that would mean starting in the blue area, then green, then yellow. You could probably even use a drill and a hole cutter to remove the yellow part.
Then it would be a matter of using a rasp file to even out the 'steps' to the curve that you want. Perhaps even a drum sanding attachment on a hand drill could do that part also.