The original model s was done up by a little company called S1NN. Whats unique there is being a new project altogether, the sound engineers had quite a bit of say in the fundamental design of the car as well, and unlike a lot of harman & competitor products which use artificial surround, that system was purely stereo. Ironically that company was then bought up by harman in '14 lol.

The current sound systems are allegedly designed in-house, some say they had B&O engineers do a good bit of it (not harman, actual olufsen), others say they still consult with s1nn, all we know is its still a pretty solid sound system, maybe not quite as good as my old model s, but definitely a solid improvement over the rivian and comparable if not better than the i5 b&w

Issue with a lot of manufacturers is they go to harman or OEM with strict speaker placements and no leeway in interior design much less chassis design, these manufacturers don't realize how important that is to proper sound design, I think the biggest example of this is the new LX with the mark levinson, lexus doesn't cheap out on higher tier models, the speakers themselves and amplification is solid, its just that speaker placement is horrible, they try to fix that in software, it results in this weird echo-y mess.

Where's with tesla they had a lot more leeway in the design, e.g. they specified the thickness of the sheet metal in the doors to prevent resonance, and then adjusted the mounting of the rest of the door components in turn, at that time you used to never see that level of design with a traditional manufacturer.

But over time it is happening more and more often - XC90, iX, mercedes 4D, rolls, the sound engineers have had a part in designing the interior and parts of the car and you can immediately tell by the speaker placement, material choices, and resulting sound.