I have done now all areas that are relevant for deadening, and some that I found are not so. I did the project bit by bit and got crazier along the way. Started with standard audio.
I first installed (day 3 of ownership) the LH speakers and deadened the doors with alubutyl similar to Dynamat. Later on, I revisited door cards to add softer acoustic material.
Then I had professionals install amps, DSP and sub. I don't know exactly how they did the high level input, but I concluded from remarks at service center (when eMMC replacement was done), that they did it right at the outputs of MCU. Apparently they were ok for SC. From there the output is wired to trunk and amps (Mosconi with integrated DSP) are in the below trunk compartment passenger side, under the rear crash rail. Custom sub enclosure is occupying rest of the passenger side rear quarter panel well. Tapping to power and extra fuses are at the 12V battery and are wired nicely all the way to back. Price of installation was fairly reasonable and at that point I had no intention to anything more.
Even after break-in and tuning, I realized the car requires a lot of deadening to sound good. Trunk and rear wheel wells deadening are very important for sub to sound high quality. Adding soft lightweight acoustic material to trunk lid was also a noticeable improvement. These are some of the best parts for reducing low pitch road noise rumble, and you could right away notice that sub volume can be increased without boominess.
While doing a wrap on dash woods, I also slightly deadened all dash panels, adding also soft material, and added felt on contact surfaces. This clearly dampened resonation from speakers in cabin. There are a lot of large cavities in the cabin, maybe because EV tech does not actually require such a massive dash and other panels we have just to make Model S look familiar enough for someone coming from ICE. Those empty spaces can effectively work like drums or other instruments with right resonating frequency.
Of the rest I've done: floors, below rear bench, pillars, selected parts of frunk, wheel wells... I'd probably do only wheel wells, unless you enjoy the project.