TL;DR The stock stereo is not as bad as you think, try a wireless Carplay/Android Auto adapter as an easy, inexpensive workaround to feed the head unit a better audio signal before you start tearing into the vehicle and making mods (unless that's your thing, in that case have at it!)
Here's 2 cents worth of advice which only applies to the LCLC trim 10 speaker stereo as that is what I have. If your goal is to spend Saturday nights in the mall parking lot battling subwoofers with the Fast and Furious crowd this ain't the stereo for you. If you are an audiophile who spends more on a turntable needle than I make in a month this ain't the stereo for you. That said I have found the quality of the stock system to be very source dependent and if you feed it properly you can actually get really decent, and loud sound from it.
The head unit has limited built-in tools to fine tune the output particularly with satellite and FM radio - just the fader, 3-d processing and the three sliders for treble, mids and bass, right? - so keep your expectations relatively low for those sources.
The native carplay and android auto interface also sound a bit flat out of the box and are not any more tweakable than the radio (I have a Samsung phone, my wife has Apple so I've used both). There is also a lack of function by design wherein when connected in wireless mode directly to the head unit the phones don't recognize that they are feeding full range speakers and rather think the music is coming from the phone speakers. As a result the low frequencies (63hz and 125 hz in particular - this is well documented around the web with regards to the Android, not sure about Apple) are disabled and the overall output level is capped..
Bear with me, I'm getting to the point -
So there are two work arounds for this. First, you can use a wired connection for Carplay/Android auto. This gets the phone to recognize that the sound is not coming from the phone speakers and lets you fully adjust the built in equalizer to adjust the signal going to the head unit which gives you fair control over the sound to fine tune to taste though the line level of the signal is still relatively quiet.
The next level solution is to insert a wireless Carplay/AA adapter in between your phone and the head unit. The benefits of this are that you can then load third party equalizer, DSP and pre-amp software that can further boost, modulate and max out the signal that will ultimately come out of the speakers.
I use a Binzie box (
Amazon.com), 99 bucks, plugs into the leftmost USB port under the HVAC controls, tucks in behind the shift lever, very inconspicuous, learning curve is very mild. There are many other options to found. Only downside I have with it is it adds a minute to two to the bootup process (the box has to connect then the phone has to connect to the box) but we're usually rockin' by the time we've backed out of the garage and are rolling down the street. Otherwise it has been plug and play.
I've loaded an app called Wavelet onto the box which gives me a parametric equalizer and 6db gain on the signal before the head unit. Your phone's built in equalizer also can work in series with the box to further adjust frequencies to taste. Because everything remains digital until the speaker outputs I haven't notice any background hissing or static from this as you would have from boosting an anologue signal in this way.
The "oldies" we listen to range from the Chili Peppers to New Order, 90's shoegazer and back to the Eagles, Queen and Pink Floyd style classic rock so not EDM or hip hop but not bass or volume shy either. With this set up there is no problem getting plenty enough volume to drown out the wind noise at 85mph, to get clear highs, good spatial definition and put the rear view mirror vibrating to the bass (enough you can see clearly) when the volume is at 40. The equalizer easily tames the mid-low frequencies that can make things sound muddy and you can still use the native head unit sliders and surround sound processing if you want to make quick overall adjustments. This has been tested and works streaming from YouTube Music, Spotify, Pandora, Tidal, the Sirius app and FLAC files downloaded to both of our phones.