I have since had a ride in one, and I must say that for car audio it is not bad at all! I was pleasantly surprised by the low level of road noise that was evident in the car, and the sound system really did sound very decent.
Of course, it is still a car, not a listening room. I still do not care for trying to do any 'listening' in a car.
Of course, it is still a car, not a listening room. I still do not care for trying to do any 'listening' in a car.