I have an in-dash 1/2 DIN EQ/Pre-Amp. The PPI PAR-245
5-Bands of EQ. Each band has a selectable freq.
The sub freq's to choose from are 30,34,36,38,40,44,46,50,52,58,66Hz
That should be enough freq choices to tame any nasty peaks in your freq response.
It also has Q values to pick from...