Thanks for the insight, all. Yeah, headphones are hard to match, but the stereo field generated by "stereo FM broadcast" has even engrossed me MORE than headphones (with the exception of Rush's "Twilight Zone" with it's panning whisper track snuck deep behind the instruments and vocals). And I couldn't agree more that car envorinment hurts the bass, which brings out the washy trebble of MP3.

So, I guess my quandry is more about the quality of the stereo field... the presence of the sound... than it is about bitrates and loud volume. Here's text from a manual for a 3D sound generation device from 1989 (which a knowledgable audio guy at work photocopied for me):

"A good test for evaluating a quality audio system involves closing one's eyes and listening for the loudspeaker locations. If one can readily point to the drivers, the system is not an accurate audio reproducer."

So, on the question of "how much to spend on a car audio system", is it possible to get such a truly engrossing sound stage that you can't pinpoint the location of the speakers? If so, I'm willing to pay to have that.