On mine i'm running them off of a alipine head unit thats giving 50x4 peak and 15x4 nominal. I have polk 6.5's in the door like this
https://soundrating.com/best-6x9-speakers/ infinity kappa 3.5's in the dash and the 6x9 kappa's in the rear. I used to install car stereos and I am certified so I can tell you that the setup I have is no where near as good as running an outboard amp. I'm waiting to put my amp in until I decide on a good subwoofer and I can get my buddy to come and measure the trunk so we can figure out how to make a box and hide everything without losing much if any trunk space. The way I have it setup does sound better than the bose system on my friends e-320 mercedes and the bose system is very good. My recommendation for now is to get a good headunit and basically do what I did with the speakers. The brand is up to you but I still definitely recommend polk or infinity The alpine head unit doesnt look anywhere near stock which pisses me off, so I am saving up to get an eclipse double din navigation system which will be custom molded into the factory slot, I will have to remove the cupholder but I dont really use it anyway. All of that will come when I finally get my amps and the sub. But enough about mine, I do get carried away. It does sound really good running off of a good aftermarket head unit. Like alpine, eclipse or maybe panasonic.
There are a lot of cool videos on YouTube, here’s one of them. Good luck