Agreed with others. Try turning off your subs for a few days and really listen to your speakers. If you want a real education is audio, try this to improve your ears; After a few days of listening with no subs listen to a CD with good clean singing vocals, like MJB , not rap. Then take the same CD into a good music store and listen to it on a decent set of speakers. Not too loud. You will hear insturments and subtle sounds like breaths and musical accents that were missing in your car. Go back outside and listen to your system again (with the subs off). Go back inside and listen to the same track inside on good speakers. Go back and forth as many times as you can.
Now you will hear why it's better to have one good set of speakers rather than 2 cheap sets of speakers.
I have no doubt your car is loud as hell, but I'd also guess your freind is right and it doesn't sound very good. Lacking in clarity and mids. More midbass is not your problem.
Get one good set of comps run off an amp and install them correctly in your doors, sealed with lots of deadening. You can install the two PG sets in the rear for screaming loud volume when you want it.