if you guys want to adjust your equalizer for the most accurate sound, then do what the fanatical home stereo/theatre guys do and go boy a sound pressure level meter (SPL) from Radioshack for $40 and then get a CD with test tones, rip them and play them in the car and measure the levels with the SPL meter. Those are the only tools you need to get it right. Using the parametric eq, you will probably want to flatten any peaks and maybe pull up any valleys. 5-bands of eq is not a lot to work with (I have 12 bands of parametric eq just for my sub at home), but it is better than none.

Now, accurate and "good" may be two different things depending on your perspective. But without the right tools, you will probably never get to find out what accurate means.