+1 again with Juleous and 90 ST.
I'd invest in a sub first before an EQ. You can usually get the sound very close to where you want it with proper placement (not many options in our small car), installation, and basic adjustments. The cabin interior is plenty padded and small; it doesn't sound like too many acoustic anomalies in it (I've yet to jam my spec analyzer in there to check). But in the end, if weirdness happens, EQ it.
