I installed an upgrade on my Cordoba a few years back, but on a budget.
1) Upgraded rear package speakers. I have noticed that OEM speakers from late model cars are both efficient and sound good. I went to the local Pick N Pull and grabbed 6X9 Infinity speakers from a later model Chrysler. After removing the original speakers, I mounted these from the underside, firing up into the original speaker holes. The mounting holes don't line up exactly, so I used drywall screws to go write into the metal of the package shelf. Such a hack, but I've done this several times previously, and it always works.
2) I like the OEM look, so I purchased an "upgraded" OEM Chrysler stereo from Ebay. There's several guys that mod them for either bluetooth use or line in. I chose a line in so I could install a satellite radio receiver. (I love the 80s Channel!)
(Note: Chrysler used the very same square shape and mounting holes from 1975 to 1997. The radios from about 1988 and up are actually quite good. The early 80s units with the "rear amp" option are tolerable, but most of the manual tune radios are pretty awful. the good news is that wiring them in is not difficult at all.)
3) I added an underseat subwoofer. No, these do not add that wonderful 20hz bass, but they do add substantial bass. By offloading the bass duties to the underseat speakers, that gives the regular speakers a little more headroom to produce everything above about 200hz. Being right under the driver's seat, you can totally feel it. I used this:
https://www.amazon.com/Kenwood-Low-...od+Subwoofer+under+seat&qid=1612982759&sr=8-5
I like what these add so much, I intend to buy one to add to my Indy Ram -- where even though the speakers are branded "Infinity", the system sounds really pathetic.
This isn't a how-to or anything, but here is how my install looks:
Cheers!