I get the opportunity to drive many new and pre-production vehicles, so I've heard many of the high end sound systems in premium vehicles. I spend a lot of time driving, and being able to listen to music on the road is important to me. Of course, a vehicle is not a concert hall or even your living room, and vehicle sound systems face a plethora of challenges unique to each different car or even changing road conditions. I have never heard a sound system in a vehicle that made me feel I was listening to a live string quartet, but taken on their own terms, I've heard a number of systems that are quite enjoyable:
The McIntosh system in the Jeep Grand Wagoneer L is pretty good, though I prefer the McIntosh version that is in the Grand Cherokee 4XE plug-in hybrid.
Meridian systems can be enjoyable. I like those in the Jaguar F-Pace and the Range Rover Defender.
Some Harmon Kardon systems actually sound good, but definitely not all. Their quality varies considerably from vehicle to vehicle. After a lot of tweaking, I've actually made peace with the HK system in my Subaru Outback XT (which has a little thicker, sound absorbing glass in the doors than other Outbacks and so is a little quieter), I find it OK, good enough that I'm not going to replace or try to upgrade it. But there are better HK systems. I have recently enjoyed the HK systems in the BMW i4 and BMW iX. I've heard several B&W systems in BMW's and only one sounded decent, but I can't recall which vehicle.
The Burmeister system in the Mercedes S580 and the EQS are both pretty enjoyable. The S580 has door tweeters that, when you turn on the system, begin to turn, screwing out into the cabin a bit. No way to A-B to see what difference it made in the sound, but it was fun to watch, and I liked the system. But I did not like the Burmeister in the MB GLS450 and some of the other MB sedans.
I remember that I enjoyed listening to the system in the Chevy Sierra High Country but I can't recall the manufacturer, and only country music sounded acceptable.
My very favorite vehicle sound system is undoubtedly the NAIM system in the Bentley Bentayga. I recall that system sounded really good in the Flying Spur Mulliner, too, but I spent more time in the Bentayga so I got to know it better there. Seriously good sound. Hell, I could live in that vehicle.
Those are a few of my favorites. Again, I'm not saying they stand on equal footing with a good home system, but then a good home system doesn't stand on equal footing with a live concert hall experience. I don't approach vehicle sound with that sort of comparison in mind. I'm just interested in whether they are enjoyable to hear, not annoying or distracting, and non-fatiguing, especially on a long drive.
Obviously, one key is a quiet vehicle. A lower noise floor improves dynamics and relieves the need for over-compressed, brittle sound to be heard above the din. There isn't a sound system in the world that I'd care to hear in a Mclaren, Corvette or Charger Hellcat Redeye; for example, they are just way too loud.
Most systems require a lot of tweaking, too. The designers usually have a different idea of appealing sound than I do. Almost all have too much bass, for example. I appreciate systems that allow simple but comprehensive adjustment, and I change the settings depending on whether I am alone or have passengers, the type of music I'm listening to or the music's source. Classical music is usually better on FM stations than, say, Sirius' classical station. There's a lot of interesting music on Sirius, but the stations are generally way too bassy, compressed and have a sort of strident, metallic quality that is hard to tune away. Streaming Quboz from my phone works well.
Bottom line is there are some pretty good sounding systems out there. But it's hard to generalize. Different systems from the same manufacturer often sound quite different. Happy motoring!