Nothing much they can do. You'll need to change the speakers and sub and probably install a DSP amplifier to fix the absolutely atrocious settings in the DSP of the factory amp. The center speaker is nearly unbearable at times.
I've tried to only change the speakers, but the settings of the system have to be redone with a DSP if you plan on playing at any real volume. For some reason they thought sending nearly the entire audio spectrum through the center 3 1/2 speaker and pumping up the treble to ungodly levels constitutes a premium sound system. If you want to see videos on this experience feel free to subscribe to my YouTube channel verdier400 and follow my progress as I stumble through this upgrade process.
Just got an Insight Touring a couple days ago and finally had a little time to break out some music, sound meter and warble tones.
I also found the center channel over-weighted. Turning off DTS Neural Sound in the "Settings-> Sound" area helped make it bearable.
Bass response was way too high by about 10dB starting around 125 Hz and very boomy, so I cranked that down to one of the lower settings. The subwoofer control kicks in around 62 Hz. That was also high, peaking at ~40 Hz. It should also probably be turned down a few notches, but I like a little extra low bass so I turned it up a few;-) There is actually decent sound pressure level even at 31 Hz on my meter, but it's dropping off considerably by 25Hz.
The sound quality overall is actually fairly comparable to some other systems I've had recently, including Toyota/JBL in the Rav4 and Prius, Kia/HK in the Niro and Hyundai/Infinity in the Ioniq. The nice thing about the Insight is the trunk. Even though it's only an 8" subwoofer with a smallish magnet and paper cone on the rear parcel shelf, it can still move more air at lower frequencies, perhaps because the trunk serves as the enclosure. The compact SUVs and hatchbacks I've had with premium audio all have tiny volume sub enclosures and the physics just doesn't allow them to get the same effective sound pressure levels down low.
Overall, the sound seems pretty decent for factory audio in the segment. I could not get close to a flat response From 200Hz down no matter the settings, but it's better than before. It's also not going to rattle the windows of the car in the next lane, but still reasonably good to my ears that aren't as critical as they were years ago. The rear parcel shelf is not well braced/damped, so it does vibrate, something that wasn't as pronounced in the hatchbacks with their tiny cargo-area subs, but of course they also couldn't play low bass as loud. I'm sure with some $$$, people can make big improvements, but keep in mind if you only do a speaker change, many factory speakers are optimized for efficiency at the cost of frequency response, especially in lower trims with lower power head units. I don't know if that's true in the premium Honda systems, but if it is, you can lose a lot of volume by putting in certain higher quality drivers.
Good luck to everyone swapping in nicer components. I wish I had better hearing to make it worth joining you!