I sent email to "ownership" basically reiterating that - on this awesome car, the audio disappoints. They responded quickly with offer of service call. Just after I'd spent a morning fooling with audio. Below is my response:
Regarding stereo... I spent about 30 minutes this am with the speaker diagram checking it out. All speakers appear to be working (including subwoofer). I believe that there are 3 elements of the audio design that make it quite different from an other auto stereo design I've ever experienced:
1) The huge balance of the speakers are forward, making the stereo very biased towards the front. Even the driver door speakers are considerably forward of driver. Most car systems have largest speakers in package shelf behind rear seat, and are therefore very biased towards the rear. In the Model S, it sounds much better with balance moved towards the rear to overcome the forward-biased design... however because the rear speakers are relatively small, if you dial it too far towards the rear, the sound degrades, and the peak volume decreases. I was pretty happy with -8 to the rear.
2) The Model S "Flat" equalization is very treble-biased. I've never before had to use equalization to get what I would consider a good "flat" EQ, but with experimentation I've found if I boost the low about +4 and mid +2, I get a good sound that I would consider flat in most systems. Without doing this, the sub-woofer barely comes into play, which is perhaps why I questioned if it is working.
3) The Dolby should only be used with Dolby 5:1 input, if at all. All it seems to do is mess up the sound of normal stereo recordings. I've used other Dolby simulation in car audio systems that enhances just about everything, but this one doesn't. It's better left off.
So, I've been able to achieve quite good sound via tweaking. But for those of us who have owned other cars with premium sound systems (which I believe accounts for vast majority of Tesla owners and reservation holders), we are not used to having to tweak to get "premium" sound quality. Expectation is it should sound good right out of the box, because that's what we're used to with other cars. I believe Tesla has 3 options: a) leave as is and let each owner discover how to adjust, b) document so owners know what to expect and how to adjust, c) change the EQ and front-rear balance "flat" settings to something more conventional - which would be achievable via software.