My 64 Chevelle had a single channel dash speaker that I replaced with a pair of Kicker 3.5 inch 2 ways, and I added a pair of 6.5 inch Kenwood 2 ways into the rear deck. Then added a 45x4 rms amp to it all and stuffed the amp under the passenger seat. It sounds very good, better than expected for the money, and I enjoyed a little proud moment for myself knowing that it's been about 20 years since I did anything like that. I forgot how frustrating, tedious, but also enjoyable it can be.
My 2021 Sorento has a 6.5 speaker in each of the 4 doors, and a pair of tweeters in the A pillar. It sounds...very mediocre. I have been toying with replacing the 4 door drivers with upgraded 2ways, and adding that same 45x4 amp I used in my Chevy. Also thinking about a powered subwoofer somewhere in the car. I could probably get away with it for cheap, $120 for speakers, $140 for the amp, $120 for the bass, $50 for wiring. The trouble is that the battery is in the spare tire compartment and I would have to tap into speaker wires in the dash behind the giant LCD screen. The time commitment, and pulling apart a brand new car is killing all my motivation to do it. It's more disassembly than I would like to do.
Maybe I can throw $500 of gear into an Amazon wishlist and send it over to the lady friend. If she green lights it enough to spend the money on it, then the decision is made for me lol