He did say 'good' car stereos.
Anyway, most half-decent MP3 CD players have an EQ. My JVC SH99R does - ok, it's only 3 band, but it is user-configurable, including width of bands. New JVC 909 has 7 band equaliser, iirc. As do Pioneer units, and I'm sure many others. They do have rock, jazz, etc. 'preset' settings, which are all universally crap, but you can make your own as well.
And the JVC and Pioneer units both have EQ presets that can vary by source - so I have User 1 on CD playing and Auxiliary Input from empeg, and User 2 on FM radio. Switches automatically.
Cheers,
A.