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Online Hearing Test ? Powered by Beltone
What type of music do you have a problem with? Too much what or not enough whatever?
Not much you can do with silly head unit setting options as automakers, and their fancy stereo suppliers, will optimize the sound system for the acoustics of the vehicle and the pathetic speaker quality chosen. With their unnecessary bazillion speaker locations, the headunit/amp will usually have optimizing/soundprocessing built-in and tuned to the car.
It is what it is unless you want to rip it all out and start from scratch.
Some might be content with simply upgrading speakers. Metal type tweeters for those that like screamers(overbearing detailed highs). Silk/soft/textile tweeters for those of us that like sweet smooth sound. Paper vs poly vs blended mids/woofers have different sounds.... Others simply wrap the car in soundproofing to improve the quality of the stock system. Yes, soundproofing doors/hatch/floors/firewall, some thick undercarriage rustproofing,.... can drop interior noise and help make the stock system sound pretty good.
I wish that automakers would leave an empty double din dash hole and larger speaker locations so that I can use whatever I want. Radio delete option is long gone!
With or without subwoofer depends on options. So, read your window sticker and look in the car. I'm guessing that OP's limited/ultimate/infinity should have it. If there isn't enough bass, than their isn't enough power or the subwoofer is a mass produced joke. And yes, most automakers subwoofers fail early if used excessively, and are grossly overpriced if out of warranty, which is why many adapt aftermarket replacements.
Test the speakers for frequency range. Remove the speakers, measure them for size, resistance, frequency range impedance, Klippel, ....and find suitable replacements for better efficiency, output, sound quality or the opposite. Or simple do a hit and run parts replacement for your music type until you find what you like.
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Imaging will come from the middle speaker and why its too bright. The solution is a simply L-pad. Another option is to remove the speaker, take some measurements, and replace it with a less annoying (less efficient or different material) speaker. I'm a fan of silk and pulp-paper. I find that too many use overly annoying speaker materials that don't sound right, usually for longevity life in an auto environment, or simply because of the price point and output.
Bose, Infinity, BostonAcoustics, JBL, Harman, ..... do produce excellent OE upgraded systems. Problem is, they can't make up for every type of music, every source of music, every owners expectations, and obviously every ear drum. They are trying too hard to give owners that stadium, music hall, concert sounds BS which isn't realistic or natural, while trying to cater to every passenger location. Silly!