It's ALL about the enclosure with subs. A different size box will make the same sub sound completely different. While yes, some are designed to not need one, the enclosure definitely counts in most cases
The electronic manufacturers have always made factory systems along with their aftermarket systems. The aftermarket used to always have the most up to date features/technology and the factory sometimes was a few years behind with that same technology. The vehicle manufactures weren’t happy with that and they also were losing money not being able to offer the same features/technology the aftermarket was given. So the vehicle manufacturers succeeded by making proprietary data bus systems to control most functions of the vehicle including the car stereo. So companies that made aftermarket gear too were forced to get almost completely in bed with the vehicle manufacturers to make money and make systems for their new vehicles. This type of new relationship between them allows for new vehicles to get the best of both worlds as far as profit and the newest technology. It leaves not too many easy ways to upgrade your system unless a aftermarket company like Metra etc. comes out with system integrators. To be able to install aftermarket gear without possibly also losing factory features/functions (other than the car stereos features) you already have. This is the current state of car electronic’s integration.
As @alvav points out, you can't do a one-for-one swap, but I checked with a white noise track and PC-based signal analyzer and the full range 20-20khz is sent to the 6 1/2" door speakers. As such, you can wire a component set into this factory harness and run a separate wire from the component crossover to the tweeter location. The front doors get a lot more power than the rear doors, so you don't get much bang for your buck by replacing the rears, but you may want to do it for completeness. I replaced mine with Alpine R-S65Cs and the difference was very noticeable across the entire spectrum, but mostly at the extreme low and high ends and at higher volumes. I had to get a little creative with the tweeter mounting, but that will likely be the case with any aftermarket tweeter. For the sub, the biggest restriction is the 8" width and fairly shallow depth of the factory enclosure. I was able to stuff an Alpine R subwoofer into this box, but it took a lot of cutting and re-sealing to get it to fit. I would recommend the Alpine S or Kicker low profile instead (use Crutchfield's fitment tool).
I have a JL Audio 8w3 in the oem box and believe me that sub hits hard even in the oem box and no rattles to be heard. The oem box is pretty good once sealed.
